Electron source manufacturing method

Abstract

The present invention provides a method for manufacturing an electron source having a structure in which a tip of an electron-emitting material is directly bonded to a tungsten filament. [Solution] A method for manufacturing an electron source includes the steps of sandwiching a workpiece, which is superimposed so that the tip of an electron-emitting material and the tungsten filament are in direct contact with each other, between a pair of welding electrodes, and welding the tip and the tungsten filament by applying a pressing force to the workpiece with the pair of welding electrodes while passing an electric current through the workpiece, and the thickness of the workpiece is in the range of 50 to 500 μm.

Description

[Technical Field]

[0001] The present disclosure relates to an electron source, a method for manufacturing the same, and an apparatus including the electron source. [Background technology]

[0002] Electron sources are used in, for example, electron microscopes and semiconductor inspection devices. Electron sources have a tip made of an electron-emitting material. Specific examples of electron-emitting materials include single crystals of LaB6 (lanthanum hexaboride), single crystals of HfC, and IrCe compounds.

[0003] An electron source using a LaB6 single crystal, for example, is composed of a LaB6 single crystal chip, a tungsten filament for heating the chip by passing current through it, and a bonding material for fixing the chip to the tungsten filament. Patent Document 1 (Production Example 1) describes providing an intermediate layer on the lower side of the LaB6 single crystal chip using a paste containing TaC powder, and providing a support metal layer using Ta foil. In this Production Example 1, a thermionic emission cathode is assembled by spot welding a 150 μm diameter W wire to the support metal layer. Patent Document 2 (Patent Document 2) describes a sintered material for a cathode component for generating an electron beam, containing at least 90 mass% of a compound consisting of iridium and cerium. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 1-7450 [Patent Document 2] Patent No. 6805306 Summary of the Invention [Problem to be solved by the invention]

[0005] When a layer containing tantalum (Ta) is interposed between the LaB6 tip and the tungsten filament (W wire), as in Manufacturing Example 1 of Patent Document 1, the tantalum reacts with LaB6 during electrical heating, degrading the vacuum level and causing cathode emission instability. Therefore, a structure in which the electron-emitting material tip is directly bonded to the tungsten filament is desirable. However, in the past, it was not possible to firmly bond the electron-emitting material tip and the tungsten filament by welding, which posed a risk of the tip falling off. For this reason, electron sources with such a structure have not yet been put into practical use.

[0006] The present disclosure provides a method for manufacturing an electron source having a structure in which a tip of an electron-emitting material is directly bonded to a tungsten filament, and also provides an electron source and an apparatus including the same that can suppress deterioration of the vacuum level and obtain a stable emission current compared to conventional electron sources that use tantalum to secure the tip. [Means for solving the problem]

[0007] A method for manufacturing an electron source according to one aspect of the present disclosure includes the steps of sandwiching a pair of welding electrodes overlaid workpieces so that a tip of an electron-emitting material and a tungsten filament are in direct contact with each other, and applying a current while applying a pressing force to the workpieces with the pair of welding electrodes to weld the tip and the tungsten filament, the thickness of the workpieces being in the range of 50 to 500 μm. Examples of electron-emitting materials include LaB6 single crystal, HfC single crystal, and IrCe compounds. Examples of IrCe compounds include Ir2Ce, Ir3Ce, Ir7Ce2, and Ir5Ce.

[0008] The inventors attempted to directly weld a tip of an electron-emitting material (single crystal of LaB6) to a tungsten filament using a resistance welding machine configured as shown in Figures 3(a) and 3(b). As a result, if the thickness of the workpiece (total thickness of the tip and tungsten filament) is in the range of 50 to 500 μm, it is possible to locally heat the workpiece to a high temperature by passing current through a pair of welding electrodes, and to firmly join the tip and tungsten filament by welding.

[0009] The cross-sectional shape of the portion of the tip that is welded to the tungsten filament is, for example, a square or rectangle with a side length of 10 to 300 μm.

[0010] An electron source according to one aspect of the present disclosure includes a tip of an electron-emitting material, a tungsten filament, and a welded portion where the tip and the tungsten filament are directly joined, the welded portion having a thickness of 50 to 500 μm. Because the tip and the tungsten filament are directly joined, deterioration of the vacuum level can be suppressed compared to conventional electron sources in which a layer containing tantalum is interposed between the tip and the tungsten filament, and a stable emission current can be obtained.

[0011] The tungsten filament in the present disclosure may contain elements other than tungsten (for example, rhenium, aluminum, silicon, and potassium) depending on the required performance.

[0012] An apparatus according to one aspect of the present disclosure includes the above-described electron source. Examples of apparatuses including an electron source include electron microscopes, semiconductor manufacturing apparatuses, and inspection apparatuses. [Effects of the Invention]

[0013] According to the present disclosure, there is provided a method for manufacturing an electron source having a structure in which a tip of an electron-emitting material is directly bonded to a tungsten filament, and also, according to the present disclosure, there is provided an electron source and an apparatus including the same that can suppress deterioration of the vacuum degree and obtain a stable emission current compared to conventional electron sources that use tantalum to fix the tip. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a plan view schematically illustrating an embodiment of an electron source according to the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view schematically showing a welded portion in the electron source shown in FIG. [Figure 3] Figure 3(a) is a cross-sectional view that shows a state in which overlapping workpieces are sandwiched between a pair of welding electrodes so that the tip and tungsten filament are in direct contact with each other, and Figure 3(b) is a cross-sectional view that shows a state in which the tip and tungsten filament are welded by applying a pressing force to the workpieces with the pair of welding electrodes while passing an electric current through them. [Figure 4] FIG. 4 is a cross-sectional view schematically showing another embodiment of the welded portion in the electron source. [Figure 5] FIG. 5 is a SEM photograph showing the electron source according to the first embodiment. [Figure 6] FIG. 6 is a SEM photograph showing the electron source according to the second embodiment. [Figure 7] FIG. 7 is a SEM photograph showing the electron source according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following description, the same elements or elements having the same functions will be designated by the same reference numerals, and duplicated descriptions will be omitted. Note that the present invention is not limited to the following embodiments.

[0016] <Electron source> Fig. 1 is a plan view schematically showing an electron source according to this embodiment. The electron source 10 shown in Fig. 1 includes a LaB6 tip 1, a tungsten filament 2, and a welded portion 3 where the tip 1 and the tungsten filament 2 are directly joined. The tip 1 is fixed by welding to the top of the tungsten filament 2, which is bent into a loop. Apparatuses that include the electron source 10 include electron microscopes, semiconductor manufacturing equipment, inspection equipment, and processing equipment.

[0017] The tip 1 emits electrons when heated by passing current through the tungsten filament 2. The tip 1 is made of a single crystal of LaB6, which is easy to emit electrons. <100> It is preferably a single crystal processed so that its orientation coincides with the electron emission direction. The side of the tip 1 is preferably a (100) crystal plane, as this is thought to slow the evaporation rate. The tip 1 has a roughly rectangular parallelepiped shape. The tip end of the tip 1 may be processed into a cone or a square pyramid shape. There are no particular restrictions on the shape of the tip 1, and it can be formed into the desired shape by electrical discharge machining or the like.

[0018] The tungsten filament 2 heats the tip 1 when current is applied. The tungsten filament 2 may contain elements other than tungsten (for example, rhenium, aluminum, silicon, and potassium) depending on the required performance. The tungsten filament 2 may be doped with an alkali metal (for example, potassium) for structural stabilization. When the tungsten filament 2 contains rhenium, the rhenium content of the tungsten filament 2 is, for example, 2 to 30 mass %, or may be 2 to 10 mass %, or 2 to 5 mass %. Rhenium has the effect of increasing the electrical resistivity of the tungsten filament 2.

[0019] The welded portion 3 is a portion where the tip 1 and the tungsten filament 2 are joined by welding. The welded portion 3 is formed by heating and melting at least one of the tip 1 and the tungsten filament 2, and then solidifying the melted portion. The thickness of the welded portion 3 (thickness T3 in FIG. 2) is, for example, 50 to 500 μm, and may be 50 to 400 μm or 110 to 250 μm. The melting point of the tip 1 is, for example, about 2210°C. The melting point of the tungsten filament 2 is, for example, about 3422°C.

[0020] <Electron source manufacturing method> Next, we will explain the method for manufacturing the electron source 10. The electron source 10 is manufactured through the following steps. (A) A process in which a workpiece 5, which is superimposed so that the tip 1 and the tungsten filament 2 are in direct contact with each other, is sandwiched between a pair of welding electrodes 6a and 6b (see FIG. 3(a)). (B) A process of welding the tip 1 and the tungsten filament 2 by applying a pressing force to the workpiece 5 with a pair of welding electrodes 6a, 6b while passing an electric current (see FIG. 3(b)).

[0021] In step (A), the thickness of the workpiece 5 (the total thickness of the tip 1 and the tungsten filament 2, thickness T5 in FIG. 3(a)) is in the range of 50 to 500 μm, preferably 170 to 400 μm, and may be 180 to 350 μm or 180 to 280 μm. The thickness of the workpiece 5 is the same as the distance between the pair of welding electrodes 6a, 6b that sandwich the workpiece 5 in step (A). When the thickness of the workpiece 5 (the distance between the pair of welding electrodes 6a, 6b) is in the above range, the workpiece 5 can be locally heated to a high temperature by passing current through the pair of welding electrodes 6a, 6b, and the tip 1 and the tungsten filament 2 can be firmly joined by welding.

[0022] The cross-sectional shape of the tip 1 at the portion to be welded to the tungsten filament 2 is, for example, a square or rectangle with a side length of 10 to 300 μm. The side length is preferably 60 to 250 μm, and may be 60 to 200 μm or 70 to 150 μm. The cross-sectional shape of the tip 1 at the portion to be welded to the tungsten filament 2 may be, for example, a circle or an ellipse. In this case, the thickness of the tip 1 in the welding direction (thickness T1 in FIG. 3(a)) is preferably 60 to 250 μm, and may be 60 to 200 μm or 70 to 150 μm. The arrow A in FIG. 3(a) indicates the "welding direction."

[0023] The cross-sectional shape of the portion of the tungsten filament 2 that is welded to the tip 1 is, for example, circular or elliptical. The thickness of the tungsten filament 2 in the welding direction (thickness T2 in FIG. 3(a)) is preferably 60 to 250 μm, and may be 60 to 200 μm or 70 to 150 μm. The cross-sectional shape of the portion of the tungsten filament 2 that is welded to the tip 1 may be, for example, square or rectangular. In this case, the thickness of the tungsten filament 2 in the welding direction is preferably 60 to 250 μm, and may be 60 to 200 μm or 70 to 150 μm.

[0024] The ratio T1 / T2 of the thickness T1 of the tip 1 to the thickness T2 of the tungsten filament 2 is preferably 0.6 to 1.4, and more preferably 0.8 to 1.3. When the ratio T1 / T2 is within the above range, the region of the workpiece 5 including the interface between the tip 1 and the tungsten filament 2 can be efficiently heated to a high temperature.

[0025] In step (B), the heating temperature can be adjusted by adjusting the current flowing from the pair of welding electrodes 6a, 6b to the workpiece 5. It is sufficient to locally melt at least one of the tip 1 and the tungsten filament 2 by heating through current flow, and it is preferable to locally melt both the tip 1 and the tungsten filament 2. The pressing force applied to the workpiece 5 from the pair of welding electrodes 6a, 6b should be set to a strength and time sufficient to firmly join the tip 1 and the tungsten filament 2. In FIG. 3(b), arrow E indicates the direction of current flow, and arrow F indicates the direction of pressing force.

[0026] The electron source manufactured by the step (B) may have a configuration in which the tip 1 is embedded in the tungsten filament 2 as shown in Fig. 2, or may have a configuration in which the tip 1 is bonded to the surface of the tungsten filament 2A as shown in Fig. 4. The tungsten filament 2A shown in Fig. 4 has a rectangular cross section.

[0027] In the above embodiment, the tip 1 is made of a single crystal of LaB6, but the tip 1 may be made of a single crystal of HfC (melting point: 3890°C) or an IrCe compound (e.g., Ir2Ce, Ir3Ce, Ir7Ce2, Ir5Ce). Even when these electron-emitting materials are used for the tip 1, the tip and the tungsten filament can be firmly joined by welding. [Example]

[0028] The present disclosure will be described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0029] Example 1 LaB6 tips and tungsten filaments of the following sizes were prepared. <LaB6のチップ> Thickness T1: 90μm Width: 90μm Length: 1000μm <Tungsten filament> Diameter (thickness T2): 127 μm Tungsten purity: 99.999% by mass or more

[0030] The tip and tungsten filament were directly welded as follows. First, the tip and tungsten filament were overlapped so that they were in direct contact, and then sandwiched between a pair of welding electrodes (see Fig. 3(a)). The tip and tungsten filament were welded together by applying pressure to them with the pair of welding electrodes while passing an electric current (see Fig. 3(b)). The welding current was set so that the temperature at the interface between the tip and tungsten filament exceeded 3422°C (the melting point of tungsten). As a result, as shown in the SEM photograph in Fig. 5, an electron source was obtained in which the tip was embedded in the tungsten filament and firmly bonded to it.

[0031] (Comparative Example) LaB6 tips and tungsten filaments of the following sizes were prepared. <LaB6のチップ> Thickness T1: 500μm ·Width: 750μm Length: 1500μm <Tungsten filament> Diameter (thickness T2): 127 μm Tungsten purity: 99.999% by mass or more

[0032] An attempt was made to weld the tip and tungsten filament in the same manner as in Example 1. Although the setting of the welding current was changed in various ways to heat the tip and the tungsten filament, it was not possible to weld the two together.

[0033] Example 2 HfC chips and tungsten filaments of the following sizes were prepared. <HfCのチップ> Thickness T1: 90μm Width: 90μm Length: 1000μm <Tungsten filament> · Diameter (thickness T2): 127 μm · Tungsten purity: 99.999 mass % or more

[0034] The welding of the chip and the tungsten filament was attempted in the same manner as in Example 1. The welding current was set so that the temperature at the interface between the chip and the tungsten filament exceeded the melting point of tungsten, 3422 °C. As a result, as shown in the SEM photograph of Fig. 6, an electron source in which a part of the chip was embedded in the tungsten filament and the two were firmly joined was obtained.

[0035] (Example 3) A chip of IrCe compound (Ir7Ce2) and a tungsten filament of the following sizes were prepared. <Chip of IrCe compound> · Thickness T1: 90 μm · Width: 90 μm · Length: 1000 μm <Tungsten filament> · Diameter (thickness T2): 127 μm · Tungsten purity: 99.999 mass % or more

[0036] The welding of the chip and the tungsten filament was attempted in the same manner as in Example 1. The welding current was set so that the temperature at the interface between the chip and the tungsten filament exceeded the melting point of tungsten, 3422 °C. As a result, as shown in the SEM photograph of Fig. 7, an electron source in which the chip was embedded in the tungsten filament and the two were firmly joined was obtained.

Explanation of symbols

[0037] 1… Chip, 2, 2A… Tungsten filament, 3… Welding part, 5… Welded object, 6a, 6b… Pair of welding electrodes, 10… Electron source.

Claims

1. a step of sandwiching the workpieces, which are overlapped so that the tip of the electron emitting material and the tungsten filament are in direct contact with each other, between a pair of welding electrodes; a step of welding the tip and the tungsten filament together by applying a pressing force to the workpiece with the pair of welding electrodes while passing a current therethrough; Including, The thickness of the workpiece in the welding direction is 170 to 500 μm, The electron emitting material is LaB ６ and The thickness of the tip in the welding direction is 60 to 250 μm, The thickness of the tungsten filament in the welding direction is 60 to 250 μm, A method for manufacturing an electron source, wherein a ratio (T1 / T2) of a thickness T1 of the tip in a welding direction to a thickness T2 of the tungsten filament in a welding direction is 0.6 to 1.

4.

2. 2. The method for manufacturing an electron source according to claim 1, wherein a cross-sectional shape of the portion of the tip that is welded to the tungsten filament is square or rectangular.

3. 3. The method for manufacturing an electron source according to claim 1, wherein the thickness of the workpiece in the welding direction is 280 [mu]m or less.

4. 4. The method for manufacturing an electron source according to claim 1, wherein the tungsten filament contains rhenium.

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