JP2006331853A - Filament assembly and electron gun, and electron beam device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filament assembly capable of preventing the wasting or degradation of a filament caused by discharge gas from a base so that a life of the filament is not unnecessarily shortened even if radiation heat or electronic collisions are generated from a heated filament. <P>SOLUTION: The filament assembly 11 is equipped with a base 12, a filament supporting part 13 attached to the base 12 and a filament 15 supported by the filament supporting part 13. A cover 17 for gas discharging prevention from the base 12 is formed on a base surface 12a at a side where the filament 15 is arranged. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a filament assembly for emitting electrons, an electron gun including the filament assembly, and an electron beam apparatus including the electron gun.

  In an electron beam apparatus such as a scanning electron microscope, a sample is irradiated with an electron beam, thereby acquiring information on the sample or performing predetermined processing on the sample. Such an electron beam apparatus is provided with an electron gun for emitting an electron beam toward a sample while being accelerated at a predetermined acceleration voltage.

  Among these electron guns, there is a thermionic gun using a thermionic emission filament. This thermionic gun includes a filament assembly having a thermionic emission filament (hereinafter referred to as a filament).

  The filament assembly includes a pedestal, a filament support attached to the pedestal, and a filament supported by the filament support. An example of the filament is a hairpin shape made of polycrystalline tungsten (W).

  Then, after the thermoelectron gun is mounted on the electron beam apparatus, the inside of the thermoelectron gun is evacuated, and a heating current is passed through the filament in a predetermined vacuum atmosphere. Heat to about 2700 ° C.

  Thermoelectrons are emitted from the tip of the filament thus heated. The emitted thermoelectrons are accelerated by a predetermined acceleration voltage in the thermoelectron gun to become an electron beam. This electron beam is irradiated onto a sample disposed in the electron beam apparatus via an electron optical system provided in the electron beam apparatus.

  When the use of the thermoelectron gun is continued in a state where the tip of the filament is heated in this way, a phenomenon occurs that the filament reaches its life and breaks. In such a case, the filament attached to the thermionic gun is exchanged.

  The average life of the filament is about 50 to 100 hours in the above example (hairpin-shaped filament). Therefore, it is desired to increase the average life and reduce the replacement frequency of the filament.

  For the purpose of extending the average life of the thermionic emission filament, it has also been proposed to laminate a plurality of metal films on the surface of the filament from the inside to the outside in the descending order of melting point (see Patent Document 1). .

JP 11-67055 A

If the use of the thermoelectron gun mounted on the electron beam device is continued, the surface of the pedestal located on the filament side is heated by radiant heat and electron collision from the filament heated in a vacuum atmosphere in the thermoelectron gun. The Rukoto. Here, since this pedestal is made of alumina (Al ₂ O ₃ ), oxygen contained in the pedestal is released to the filament side as a release gas from the heated pedestal.

  As described above, the oxygen released from the pedestal causes consumption and deterioration of the heated filament while the use of the thermoelectron gun is continued, and shortens the life of the filament. It should be noted that as the emitted gas that causes the exhaustion and deterioration of the filament during the use of the thermoelectron gun, water vapor and the like can be considered in addition to oxygen.

  The present invention has been made in view of such a point, and even if radiant heat or electron collision from a heated filament occurs, it is possible to prevent the filament from being consumed or deteriorated due to the gas released from the pedestal. It is an object of the present invention to provide a filament assembly that does not unnecessarily shorten the life of the filament.

  It is another object of the present invention to provide an electron gun provided with such a filament assembly and an electron beam apparatus provided with the electron gun.

  One filament assembly according to the present invention includes a pedestal, a filament support portion attached to the pedestal, and a filament supported by the filament support portion. A coating for preventing gas release from the pedestal is formed.

  Another filament assembly according to the present invention is a filament assembly comprising a pedestal, a filament support attached to the pedestal, and a filament supported by the filament support, wherein the pedestal is made of silicon nitride. And

  Furthermore, an electron gun according to the present invention includes any one of the above-described filament assemblies.

  And the electron beam apparatus based on this invention comprised the said electron gun, It is characterized by the above-mentioned.

  In one filament assembly of the present invention, a coating for preventing gas emission from the pedestal is formed on the surface of the pedestal on the side where the filament is disposed.

  Therefore, even if radiant heat or electron collision occurs from the heated filament, the gas released from the pedestal is blocked by the coating film for preventing gas emission, and the filament is consumed and deteriorated due to the gas released from the pedestal. Can be prevented. Thereby, it can prevent that the lifetime of a filament is shortened unnecessarily.

  In another filament assembly of the present invention, the base is made of silicon nitride.

  Therefore, since oxygen is not included in the composition of the material constituting the pedestal, even if radiant heat or electron collision occurs from the heated filament, a release gas such as oxygen is not released from the pedestal. Thereby, consumption and deterioration of the filament can be prevented, and the life of the filament can be prevented from being unnecessarily shortened.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an electron beam apparatus according to the present invention. In the present embodiment, the electron beam apparatus is an example of a scanning electron microscope.

  The electron beam apparatus includes an electron gun 1. The electron gun 1 includes a filament assembly (not shown), and electrons are extracted from the filament attached to the filament assembly.

In the present embodiment, the electron gun 1 is a thermionic gun using a thermionic emission filament. In this thermoelectron gun, a heating current (for example, 2 to 3 A) is supplied to a filament provided inside, and the tip of the filament described later is heated to about 2700 to 2800 ° C. At this time, the inside of the thermionic gun is evacuated, and the filament is placed in a predetermined vacuum atmosphere (atmosphere having a pressure of 1 × 10 ⁻³ Pa or less). In this state, electrons are extracted from the filament.

  The electrons extracted in this way are accelerated in the electron gun 1 and emitted from the electron gun 1 toward the sample 6 as an electron beam 7.

  The electron beam 7 emitted from the electron gun 1 is irradiated in a state of being finely focused on the sample 6 by the focusing lens 2 and the objective lens 4. At this time, the electron beam 7 is appropriately deflected by the scanning coil 3. As a result, the electron beam 1 scans the sample 6. Here, the focusing lens 2, the scanning coil 3, and the objective lens 4 constitute an electron optical system 9.

  From the sample 6 scanned with the electron beam 7, detected electrons 8 such as secondary electrons are generated. The detected electrons 8 are detected by the electron detector 5. Then, a scanning image of the sample 8 is created based on the detection result of the detected electrons 8 by the electron detector 5.

  As described above, the electron gun 1 mounted on the electron beam apparatus having the above-described configuration includes the filament assembly.

  The configuration of the first embodiment of the filament assembly according to the present invention is shown in FIG. In the figure, reference numeral 11 denotes a filament assembly.

The filament assembly 11 includes a pedestal 12 made of an insulator. The pedestal 12 is made of alumina (Al ₂ O ₃ ). Two stem poles 13 (filament support portions) made of metal are attached so as to penetrate the pedestal 12. These stem poles 13 are welded to the base 12 with a welding material 14.

  A proximal end portion of a filament 15 made of polycrystalline tungsten (W) is attached to the distal end portion 13 a of the stem pole 13. The filament 15 has a pair pin shape. Then, electrons are drawn out from the distal end portion 16 of the filament 15 having a hairpin shape. The diameter of the filament 15 is 100 to 150 μm.

  In the present invention, a metal film (a film for preventing gas release) 17 is formed on the surface (base surface) 12a of the base 12 on the side where the filament 15 is disposed. The coating 17 is made of gold (Au), platinum (Pt), or titanium (Ti), and has a thickness of 10 to 1000 nm.

  The coating film 17 is formed by ion plating, sputtering, or vapor deposition. In this case, masking is applied to the peripheral portion 17a of one stem pole 13 on the pedestal surface 12a. Thereby, the short circuit between both stem poles 13 is prevented by the coating 17.

  In the electron gun 1 having such a filament assembly 11, even if radiant heat or electron collision from the heated filament 15 occurs, the gas released from the pedestal 12 is blocked by the coating 17 for preventing gas emission. Thus, it is possible to prevent the filament 15 from being consumed or deteriorated due to the gas released from the base 12. Thereby, it is possible to prevent the life of the filament 15 from being unnecessarily shortened.

  As shown in FIG. 3, when the filament assembly 11 is mounted on the electron gun 1, a film 17 may be formed on the tip 16 of the filament 15. In this case, the coating film 17 formed on the tip portion 16 is melted and evaporated by heating in the vacuum atmosphere, and there is no problem in the emission of electrons from the tip portion 16.

  Further, as shown in FIG. 4, a film 17 may also be formed on the surface of a frame 18 for holding the periphery of the pedestal 12.

  When the coating 17 is provided on the pedestal surface 12a of the pedestal 12 constituting the filament assembly 11 shown in FIGS. 2 and 4, after the filament assembly 11 is assembled, ion plating, sputtering, or vapor deposition is performed on the pedestal surface 12a. Apply.

Next, a configuration of a modification of the filament assembly in the present invention is shown in FIG. In this figure, the pedestal 12 is made of alumina in the same manner as described above, but an insulating coating (a coating for preventing gas release) 19 made of silicon nitride (Si ₃ N ₄ ) is formed on the pedestal surface 12. ing.

  Such a film 19 made of silicon nitride can be formed by a CVD method. In this case, since silicon nitride has an insulating property, it is not necessary to perform the above-described masking on the peripheral portion of one stem pole 13, and the coating film 19 can be formed efficiently.

Also in the electron gun 1 having such a filament assembly 11, when radiation heat from the heated filament 15 or electron collision occurs, the gas released from the base 12 is blocked by the coating 19 for preventing gas emission. Thus, it is possible to prevent the filament 15 from being consumed or deteriorated due to the gas released from the base 12. Thereby, it is possible to prevent the life of the filament 15 from being unnecessarily shortened. Furthermore, FIG. 6 shows a configuration of a second embodiment of the filament assembly according to the present invention. The pedestal 12 in each of the above examples is made of alumina, but the pedestal 12b in the present embodiment is made of silicon nitride.

  Therefore, in the present embodiment, oxygen is not included in the composition of the material constituting the pedestal 12b. Therefore, even if radiant heat from the heated filament 15 or electron collision occurs, a release gas such as oxygen is not released from the pedestal 12b. Thereby, consumption and deterioration of the filament 15 can be prevented, and the life of the filament 15 can be prevented from being unnecessarily shortened.

  In each of the above examples, the filament 15 has the form of a hairpin filament. However, the present invention is not limited to this. For example, the filament 15 may be any one of a point filament, a sharped filament, and a semipoint filament. Good. Further, the filament 15 is not limited to one made of polycrystalline tungsten, but may be made of an alloy made of tungsten and rhenium (Re), for example.

  Furthermore, although the electron gun 1 has been described as an example of a thermionic gun, it can also be applied to an example of a hot cathode field emission gun or a cold cathode field emission gun.

It is a schematic block diagram which shows the electron beam apparatus in this invention. It is a figure which shows the structure of the filament assembly in 1st Example of this invention. It is a principal part enlarged view which shows the front-end | tip part of a filament. It is a figure which shows the structure of the filament assembly provided with a frame around the base. It is a figure which shows the structure of the filament assembly in the modification of this invention. It is a figure which shows the structure of the filament assembly in 2nd Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electron gun, 2 ... Focusing lens, 3 ... Scanning coil, 4 ... Objective lens, 5 ... Electron detector, 6 ... Sample, 7 ... Electron beam, 8 ... Electron to be detected, 11 ... Filament assembly, 12 ... Base 12a ... pedestal surface, 13 ... stem pole, 14 ... welding material, 15 ... filament, 16 ... filament tip, 17 ... coating, 18 ... frame, 19 ... coating

Claims (11)

In a filament assembly comprising a pedestal, a filament support attached to the pedestal, and a filament supported by the filament support, a coating for preventing gas emission from the pedestal is provided on the surface of the pedestal on the side where the filament is disposed. A filament assembly which is formed. The filament assembly according to claim 1, wherein the coating is made of gold, platinum, or titanium. 3. The filament assembly according to claim 2, wherein the coating is formed with a thickness of 10 to 1000 nm. 4. The filament assembly according to claim 2, wherein the coating is formed by ion plating, sputtering, or vapor deposition. The filament assembly according to claim 1, wherein the coating is made of silicon nitride. 6. The filament assembly according to claim 5, wherein the coating is formed by a CVD method. The filament assembly according to any one of claims 1 to 6, wherein the base is made of alumina. A filament assembly comprising a pedestal, a filament support portion attached to the pedestal, and a filament supported by the filament support portion, wherein the pedestal is made of silicon nitride. The filament assembly according to any one of claims 1 to 8, wherein the filament has one of a hairpin filament, a point filament, a sharped filament, and a semipoint filament. An electron gun comprising the filament assembly according to claim 1. An electron beam apparatus comprising the electron gun according to claim 10.

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