Insulating insulators, charged particle guns, charged particle beam devices

Abstract

The purpose of the present disclosure is to provide an insulator with which it is possible to shorten the conditioning time and reduce withstand voltage defects in cases where the potential difference between electrodes is approximately several tens of kV. An insulator according to the present disclosure comprises an insulation material part and a glass film. The boundary between the insulating material part and an end part of a cathode on the side thereof facing an anode is covered by the glass film (see fig. 2).

Description

Technical Field

[0001] The present disclosure relates to an insulating gasket disposed between electrodes in a vacuum vessel.

Background Art

[0002] An electron beam or an ion beam used in an electron beam accelerator or the like provided in an electron microscope, an ion beam processing apparatus, a synchrotron radiation facility, etc. is emitted from a fine and pointed tip of an electron source or an ion source by concentrating an electric field in a vacuum on the tip. To achieve this, a plurality of electrodes having different potentials are fixed near the electron source or the ion source via insulating gaskets. The potential difference between the electrodes is often from several hundred volts to several tens of kV. In order to stably maintain such a potential difference without causing discharge, a conditioning process is required when starting up an electron gun or an ion gun.

[0003] The conditioning process repeats causing creeping discharge by concentrating an electric field on the tip of minute protrusions formed on the surface of the electrodes, and thereby disappearing the protrusions by Joule heat. As a result, since the protrusions where the electric field concentrates decrease, the voltage that can be applied between the electrodes without causing creeping discharge can be increased.

[0004] The conditioning process leads to an increase in the labor and manufacturing time required in the startup process of an electron gun or an ion gun, so shortening the process time has been an issue. Further, there is also an issue that the conditioning process does not end normally, a predetermined withstand voltage cannot be obtained, and the product is discarded as a defective product, resulting in a decrease in the yield.

[0005] Patent Document 1 discloses a method of suppressing creeping discharge by suppressing charge-up by applying vanadium-containing glass, which is a metal glass exhibiting semiconductive properties, to the entire surface of the gasket as a means for suppressing creeping discharge. Further, it is also explained that the surface of the vanadium-containing glass has a vacuum evacuation function for gas adsorption. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] US2018 / 0019096 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0007] The resistivity of the vanadium-containing glass described in Patent Document 1 is 10 6 ~10 13 The resistivity is Ω·cm. This resistivity correlates with the film thickness and corresponds to approximately several tens of micrometers to 1 nm. For example, in order to maintain an inter-electrode potential difference of several tens of kV, the metallic glass film thickness must be at least less than 1 μm. However, since the height of the irregularities on the cathode edge is on the order of micrometers, if the metallic glass film thickness is 1 μm or less, the irregular shape will remain as is. In that case, even if a conditioning process is performed, it is unavoidable that the electric field will concentrate on the protrusions on the electrode surface, leading to the problem of creepage discharge.

[0008] This disclosure has been made in view of the above-mentioned problems, and aims to provide an insulating insulator that can shorten the conditioning time and reduce voltage withstand failure when the potential difference between electrodes is several tens of kV. [Means for solving the problem]

[0009] The insulator according to this disclosure comprises an insulating material portion and a glass film, and the boundary between the end of the cathode facing the anode and the insulating material portion is covered by the glass film. [Effects of the Invention]

[0010] According to the insulating insulator described herein, when the potential difference between electrodes is several tens of kV, the conditioning period can be significantly shortened and the voltage withstand failure can be reduced. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram illustrating the physical phenomena in the conditioning process of insulating insulators. [Figure 2] This is a side view showing the structure of an insulating insulator according to Embodiment 1. [Figure 3] Figure 2 shows a model for numerically calculating the electric field strength distribution when a voltage of -10kV is applied to cathode 2 of the structure shown in Figure 2. [Figure 4] The calculation results using the model in Figure 3 are shown. [Figure 5] This is a magnified schematic diagram of the actual electrode surface. [Figure 6] This is an enlarged schematic diagram of an insulating insulator according to Embodiment 1. [Figure 7] This is an enlarged schematic diagram of the insulating insulator described in Patent Document 1. [Figure 8] This shows an example configuration in which the alumina insulator 1 of Embodiment 1 is applied to the current introduction terminal portion of the electron gun. [Figure 9] This component consists of a cylindrical aluminum insulator 1 and a ring-shaped metal part 10 bonded and fixed together by a metallizing film 8. [Figure 10] This shows an example configuration in which the alumina insulator 1 of Embodiment 1 is applied to a scanning electron microscope (SEM). [Modes for carrying out the invention]

[0012] <Conditioning Process> Figure 1 is a schematic diagram illustrating the physical phenomena in the conditioning process of insulating insulators. To facilitate understanding of this disclosure, the conditioning process will be outlined using Figure 1 before describing the embodiments of this disclosure.

[0013] The discharge in the section where the cathode 2 and the anode 5 are fixed with the alumina insulator 1 sandwiched therebetween is called creeping discharge. In a general design, the distance between the cathode and the anode is ensured in order to suppress the electric field strength so as not to cause creeping discharge. However, on the actual end face of the cathode (the end face surface on the side where the cathode 2 faces the anode 5), irregularities on the order of μm are formed, and their shapes are also various. When a negative voltage is gradually applied to the cathode 2 in this state, the electric field concentrates on the sharpest convex part, field emission electrons are generated, and creeping discharge occurs (I). At this time, the tip of this protrusion melts and disappears due to Joule heat (II). When the cathode 2 is energized again and the voltage is gradually increased, the electric field concentrates on the next sharp convex part and creeping discharge occurs (III). If this is repeated, the voltage applied to the cathode 2 increases, so this is continued until it reaches a predetermined voltage or more. The above process is called conditioning.

[0014] <Embodiment 1> FIG. 2 is a side view showing the structure of the insulating insulator according to Embodiment 1 of the present disclosure. The insulating insulator of the present embodiment is assumed to be disposed between the cathode 2 and the anode 5 in a vacuum vessel, and is composed of an alumina insulator 1 and a low melting point metal glass 3. When a negative voltage is applied to the cathode 2 formed on the surface of the alumina insulator 1 (insulating material portion) placed in a vacuum, the electric field concentrates on the triple point 4 which is the edge of the cathode 2, and field emission electrons are emitted, leading to creeping discharge. In the structure of FIG. 2, by covering the triple point 4 with the low melting point metal glass 3, the electric field concentration applied to the triple point 4 is alleviated. An example using vanadium-containing glass as the low melting point metal glass 3 will be described below.

[0015] Alumina is often used as the insulating material portion (the insulator main body portion indicated by reference numeral 1 in FIG. 2). The surface roughness of the alumina insulator 1 is about 20 μm. The cathode 2 is often nickel-plated on a metallized film of molybdenum and manganese. The low melting point metal glass 3 extends along the depth direction of FIG. 2 (the longitudinal direction of FIG. 1).

[0016] The low-melting-point metallic glass 3 covers the triple point 4 and its surrounding area. The triple point 4 is the boundary between the end of the cathode 2 facing the anode 5 and the alumina insulator 1. Therefore, the low-melting-point metallic glass 3 covers the area from (a) the top surface of the cathode 2, through (b) the boundary between the end surface of the cathode 2 and the alumina insulator 1 (triple point 4), to (c) the region between the cathode 2 and the anode 5. However, the low-melting-point metallic glass 3 is positioned so as not to electrically connect the cathode 2 and the anode 5 (i.e., it does not extend to the anode 5).

[0017] Figure 3 shows a model for numerically calculating the electric field strength distribution when a voltage of -10kV is applied to cathode 2 with the structure shown in Figure 2. The calculation was performed assuming a relative permittivity of 10 for the alumina insulator 1 and a relative permittivity of 15 for the vanadium-containing glass. The vanadium-containing glass (low melting point metallic glass 3) had a width of 400 μm to cover cathode 2 and the alumina insulator (alumina insulator 1), and a film thickness of 20 μm.

[0018] Figure 4 shows the calculation results using the model in Figure 3. As shown in the upper part of Figure 4, in the absence of vanadium-containing glass, the electric field concentrates at the cathode edge, resulting in 1.7 × 10⁻⁶ 3 This generates a strong electric field of MV / m. In contrast, when vanadium-containing glass is coated, the electric field at the cathode edge becomes 4.8 × 10⁻⁶. 2 It can be seen that the noise level is reduced to MV / m.

[0019] The lower part of Figure 4 shows the calculation results considering the wettability at the edge of the vanadium-containing glass. The boundary between the anode 5 side edge of the vanadium-containing glass (low melting point metallic glass 3) and the alumina insulator 1 (the peak around x=0.2 in the lower part of Figure 4) tends to become a secondary triple point where the electric field concentrates. However, it can be seen that this electric field is significantly smaller than the electric field at the cathode edge (x=0) in the absence of vanadium-containing glass.

[0020] The arrow on the right side of the lower part of Figure 4 indicates the electric field at the edge of the low-melting-point metallic glass 3 (around x=0.2) when the wettability of the low-melting-point metallic glass 3 is good. As the graph shows, it can be seen that the electric field near the edge can be further reduced when the wettability of the low-melting-point metallic glass is good.

[0021] The results in Figure 4 can be understood as follows: The surface shape of the low-melting-point metallic glass 3 facing the anode 5 is smoother than the surface shape of the cathode 2. That is, the radius of curvature of the surface shape of the low-melting-point metallic glass 3 is larger than the radius of curvature of the convexity formed on the surface of the cathode 2. As a result, the electric field is less likely to concentrate on the end surface of the low-melting-point metallic glass 3 on the anode 5 side, resulting in the result shown in the upper part of Figure 4. Furthermore, if the wettability of the low-melting-point metallic glass 3 is good, the surface shape becomes even smoother, so the electric field becomes even less likely to concentrate, resulting in the result shown by the two arrows in the lower part of Figure 4. The wettability should be such that the contact angle of the low-melting-point metallic glass 3 with respect to the aluminum insulator 1 is less than 90°.

[0022] Figure 5 is a magnified schematic diagram of the actual electrode surface. The calculation results explained in Figures 3 and 4 are numerical estimates based on a simplified shape. However, the actual cathode end surface has irregularities as shown in Figure 5. These irregularities are due to the surface roughness of the alumina and the grain size of the cathode metal. Since the size of these irregularities varies randomly, it is difficult to determine the localized location where the electric field concentrates when a voltage is applied to cathode 2 before discharge. Therefore, field-emission electrons are emitted from the area of ​​strongest electric field concentration, leading to surface discharge. For this reason, conditioning treatment is performed during the startup phase of electron gun manufacturing to ensure voltage withstand characteristics.

[0023] Figure 6 is an enlarged schematic diagram of an insulating insulator according to this embodiment 1. In this embodiment, as shown in Figure 6, a low-melting-point metallic glass 3 was deposited along the edge of the cathode 2 to a thickness of approximately 20 μm. With such a film thickness, the entire area near the triple point can be covered without being affected by the irregularities of the surface of the cathode 2 and the surface of the alumina insulator 1. When the vanadium-containing glass, which is a metallic glass, is heated to its softening temperature, it softens while remaining amorphous, so it adheres to the irregular shape and the surface becomes smooth, and when it returns to room temperature it solidifies while remaining amorphous. The resistivity of vanadium-containing glass with a film thickness of 20 μm is 10 6 Since the potential is approximately Ω·cm, the potential of the low-melting-point metallic glass 3 is approximately the same as that of cathode 2. This neutralizes the electric field concentration at the cathode edge and allows for the acquisition of a smooth vanadium-containing glass edge, thereby mitigating the overall electric field concentration. Consequently, this results in reduced effort and time required for conditioning.

[0024] The thickness of the low-melting-point metallic glass 3 should preferably be at least greater than the maximum height of the protrusions formed on the surface of the cathode 2 (the maximum peak height on the surface of the cathode 2 facing the anode 5). More preferably, if the portion of the low-melting-point metallic glass 3 covering the cathode 2 is thicker than the maximum thickness of the portion of the cathode 2 covered by the low-melting-point metallic glass 3, it is considered that the protrusions on the surface of the cathode 2 can be completely covered. If the standard film thickness of the cathode 2 is about 20 μm, then the film thickness of the low-melting-point metallic glass 3 should also be 20 μm.

[0025] Figure 7 is an enlarged schematic diagram of an insulating insulator described in Patent Document 1. Conventional metallic glass 7 (vanadium-containing glass) is deposited to cover the entire section between cathode 2 and anode 5. Since a voltage of minus several tens of kV or more is applied to cathode 2, the resistivity is 10 10Since a thickness of approximately Ω·cm is required, the actual film thickness becomes less than 1 μm. This eliminates the charge-up of the alumina insulator 1, but it is difficult to eliminate the irregularities of the alumina insulator 1, which are 20 μm or thicker. In that case, if a defect occurs in the film of the conventional metallic glass 7, the electric field concentrates there, causing field-emitted electrons to be generated. Furthermore, since minute protrusions of a few μm in size formed on the cathode 2, which has a film thickness of about 20 μm, are exposed, it is difficult to suppress field-emitted electrons. According to this embodiment, such field-emitted electrons can also be suppressed.

[0026] <Embodiment 1: Summary> The insulating insulator according to this embodiment 1 comprises an alumina insulator 1 and a low-melting-point metallic glass 3, the low-melting-point metallic glass 3 covering the boundary (triple point 4) between the end of the cathode 2 facing the anode 5 and the alumina insulator 1. This suppresses the concentration of the electric field on the protrusions formed on the end surface of the cathode 2, thereby shortening the conditioning process.

[0027] <Embodiment 2> Figure 8 shows an example configuration in which the alumina insulator 1 of Embodiment 1 is applied to the current introduction terminal portion of an electron gun. The pins 9 are for supplying voltage and current from the atmospheric side to the vacuum. The alumina insulator 1 and the pins 9 are bonded and fixed together with a metallizing film 8 for vacuum sealing. Since the metallizing film 8 is a conductive metal, there is a risk of surface discharge when there are multiple pins 9. Therefore, the low melting point metallic glass 6 (vanadium-containing glass) of this disclosure is applied to cover the vicinity of the edges of the metallizing film 8. There is a potential difference of several kV between the pins 9 in Figure 8, but by adopting this structure, the risk of surface discharge is greatly reduced. Therefore, the conditioning processing time can be shortened.

[0028] Figure 9 shows a component in which a cylindrical aluminum insulator 1 and a ring-shaped metal part 10 are bonded and fixed together with a metallizing film 8. This component can be applied to larger parts compared to the pin 9 described in Figure 8.

[0029] <Embodiment 3> Figure 10 shows an example configuration in which the alumina insulator 1 of Embodiment 1 is applied to a scanning electron microscope (SEM). An electron source 14 is installed at the top of the apparatus, and voltage is supplied from a power supply 19 via a feedthrough 20. The feedthrough 20 uses the pins 9 described in Embodiment 2, and a low-melting-point metallic glass 3 is applied to cover the metallization film 8 and the alumina insulator 1. An electron extraction electrode 15 is installed near the electron source 14 to extract electrons. The electron extraction electrode 15 is fixed to the column 21 via the alumina insulator 1. Since the column 21 is grounded, the electron extraction electrode 15 becomes the cathode and the column 21 becomes the anode. Therefore, the low-melting-point metallic glass 3 is applied to cover the metallization film that adheres and fixes the electron extraction electrode 15 to the alumina insulator 1 and the edges of the electron extraction electrode 15. The components from the power supply 19 to the electron extraction electrode 15 operate as an electron gun 11.

[0030] The electron beam 22 drawn from the electron source 14 is focused by the condenser lens 12 and the objective lens 13 to irradiate the sample 18. Secondary electrons 23 generated when the electron beam 22 is deflected by the deflector 16 on the sample 18 and raster scanned are detected by the secondary electron detector 17. This allows a magnified image of the sample 18 to be obtained.

[0031] <Regarding variations of this disclosure> In the embodiments described above, the insulating insulator according to the present disclosure is placed between the cathode 2 and the anode 5. When using the insulating insulator according to the present disclosure, the cathode 2 only needs to have a lower potential than the anode 5, and does not necessarily have to be at a negative potential.

[0032] In the embodiments described above, examples of applying the insulating insulator according to the Disclosure to an electron gun or scanning electron microscope have been explained, but the insulating insulator according to the Disclosure can also be applied to other charged particle guns and charged particle beam devices.

[0033] In the embodiments described above, vanadium-containing glass was given as an example of low-melting-point metallic glass 3. Vanadium-containing glass is an example of semiconducting glass or semiconducting low-melting-point metallic glass, and is composed of metal oxides (including vanadium, tungsten, etc.), but other chalcogenide glasses (including arsenic, antimony, bismuth, etc.) can also be used as low-melting-point metallic glass 3. [Explanation of Symbols]

[0034] 1. Aluminium Insulator 2 cathode 3. Low melting point metallic glass 4 Triple Point 5 Anode 7 Metallic Glass 8 Metallized film 9 pins 10 Metal parts 11. Electron gun 12 Condenser Lens 13 Objective lens 14 Electron source 15. Drawer electrodes 16 Deflector 17 Secondary electron detector 18 samples 19 Power supply 20 feedthrough 21 columns 22 Electron beam 23 Secondary electron

Claims

1. An insulating insulator placed between a cathode and an anode relative to the cathode in a vacuum container, An insulating material portion is positioned below the cathode and the anode, respectively. The system includes a glass film arranged to cover the boundary between the end of the cathode facing the anode and the insulating material portion, The glass film is composed of a material that includes at least one of semiconducting glass or semiconducting low-melting-point metallic glass. A region not covered by the glass film is located between the cathode and the anode. The thickness of the glass film is greater than the maximum peak height of the cathode. The radius of curvature of the shape of the glass film at the end is greater than the radius of curvature of the protrusion formed by the surface roughness of the cathode at the end. An insulating insulator characterized by the following features.

2. The glass film is arranged to cover the triple point that occurs at the end. The insulating insulator according to feature 1.

3. The glass film covers the boundary and is arranged so as not to electrically connect the anode and the cathode. The insulating insulator according to feature 1.

4. The glass film is arranged to cover the area from the side of the cathode that is not in contact with the insulating material portion, through the end, to the position of the insulating material portion between the cathode and the anode. The insulating insulator according to feature 1.

5. The thickness of the portion of the glass film covering the cathode is greater than the maximum thickness of the portion of the cathode covered by the glass film. The insulating insulator according to feature 1.

6. The thickness of the glass film at the aforementioned end is 20 μm or more. The insulating insulator according to feature 1.

7. The insulating insulator according to claim 1, characterized in that the contact angle of the glass film is less than 90°.

8. The insulating insulator according to claim 1, characterized in that the glass film is vanadium-containing glass.

9. The insulating insulator according to claim 1, characterized in that the insulating material portion is formed of alumina.

10. A charged particle gun characterized by comprising the insulating insulator described in claim 1.

11. A charged particle beam apparatus characterized by comprising an insulating insulator as described in claim 1.

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