JP4943641B2 - Filament assembly, electron gun, and electron beam apparatus - Google Patents

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. In this thermoelectron gun, for example, a thermoelectron emission filament (hereinafter referred to as a filament) composed of polycrystalline tungsten (W) is attached so as to have a hairpin shape, for example.

  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 supplied to the filament in a predetermined vacuum atmosphere, whereby the tip of the hairpin shape portion in the filament Is heated 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 to a sample disposed in the 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 in which 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 heat-dissipating filament, it has also been proposed to laminate a plurality of metal films on the surface of the filament from the inner side to the outer side in descending order of melting point (see Patent Document 1).

JP 11-67055 A

  After the thermoelectron gun to which the filament is attached is mounted on the electron beam apparatus, the inside thereof is evacuated as described above. Then, a heating current is supplied to the filament in a predetermined vacuum atmosphere to heat the tip of the hairpin-shaped portion until the temperature reaches the above temperature, and in this state, until thermoelectrons are stably emitted from the tip. This state is maintained (for example, about 30 minutes), and thereby aging is performed.

  In this case, before the thermoelectron gun is mounted on the electron beam apparatus, the surface of the filament attached to the thermoelectron gun is exposed to the atmosphere. Thereby, the surface of a filament will be exposed to the water vapor | steam etc. in air | atmosphere. Therefore, it is considered that a small amount of deposits such as moisture caused by water vapor in the atmosphere exist on the surface of the filament before the mounting, and a part thereof is adsorbed.

  When the aging is carried out after mounting a thermoelectron gun having a filament with minute deposits on the surface in the electron beam apparatus as described above, most of the deposits existing on the filament surface in the predetermined vacuum atmosphere. Evaporates, but some deposits (especially those adsorbed) are considered to remain in a very small amount.

  As a result, for example, if the filament is heated with a very small amount of moisture remaining on the filament surface at the time of aging, tungsten is very weak against moisture remaining on the surface at the above temperature. Sometimes the tungsten that constitutes the filament will deteriorate. For this reason, if the thermoelectron gun is used by continuously heating the filament after aging, the filament is likely to break, and the life of the filament is shortened.

  The present invention has been made in view of such points, and even when aging is performed in a state where a small amount of deposits remain on the surface of the filament, deterioration of tungsten constituting the filament can be prevented, Accordingly, an object of the present invention is to provide a filament assembly capable of extending 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.

The filament assembly according to the present invention is a filament assembly including a filament that is heated under vacuum and emits electrons, and the filament contains at least tungsten, and is melted and evaporated by heating under the vacuum. In addition, as a metal protective film to be removed from the filament surface, a film made of gold, platinum, or titanium is formed on the surface of the filament.

  In addition, an electron gun according to the present invention includes the filament assembly.

  An electron beam apparatus according to the present invention includes the electron gun.

In the present invention, the filament contains at least tungsten, and is melted and evaporated by heating under vacuum in which electrons are emitted. As a metal protective film removed from the filament surface, gold, platinum, Alternatively, a film made of titanium is formed on the surface of the filament.

  Therefore, even if the electron gun with the filament attached is mounted on the electron beam apparatus and aging is performed, deposits such as moisture due to exposure to the atmosphere before the mounting are on the protective film formed on the filament surface. Therefore, the deposit is completely removed together with the evaporation of the protective film during the aging.

  Therefore, since the aging is performed in the state where there is no deposit such as moisture on the surface of the filament containing tungsten, it is possible to prevent the tungsten constituting the filament from being deteriorated, thereby prolonging the life of the filament. it can.

  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 passed through 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 thermoelectron gun is evacuated, and the filament is placed in a predetermined vacuum atmosphere. 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 filament assembly in 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. Two stem poles 13 made of metal are provided 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. In the present embodiment, 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.

  Further, a metal protective film is formed on the surface of the filament 15 to be melted by heating to a temperature at which electrons are drawn out and emitted as described above. This metal protective film is melted by heating the filament 15 to the above temperature in a vacuum, and evaporates from the surface of the filament 15. As a result, the metal protective film is removed from the surface of the filament 15.

  An enlarged sectional view of the tip 16 of the filament 15 is shown in FIG. As shown in the figure, a metal protective film 17 is formed on the hairpin-shaped filament 15. The metal protective film 17 is made of a gold (Au) thin film in the present embodiment. The metal protective film 17 has a thickness of 10 nm to 1000 nm.

  The metal protective film 17 can be formed by an ion plating method, a sputtering method, or a vapor deposition method. In this embodiment, after the filament 15 is attached to the tip 13a of the stem pole 13 constituting the filament assembly 11 in a hairpin shape, the metal protective film 17 is formed on the surface of the filament 15 in this state. Do. At this time, a mask is provided at a predetermined position of the base 12 so that a short circuit does not occur between the two stem poles 13.

  When the metal protective film 17 is formed on the surface of the filament 15 in this way, the filament 15 is placed in a vacuum regardless of the ion plating method, sputtering method, or vapor deposition method. In this state, the metal protective film 17 is formed on the surface.

  That is, the filament assembly to which the filament 15 is attached is arranged in a vacuum chamber constituting an ion plating apparatus, sputtering apparatus, or vapor deposition apparatus, and the inside of the vacuum chamber is evacuated. Thereafter, a metal protective film 17 is formed on the surface of the filament 15 by ion plating, sputtering or vapor deposition in the vacuum chamber. When the metal protective film 17 is formed, the filament 15 is not heated, and the metal protective film 17 is formed while the filament 15 is at room temperature (20 to 25 ° C.).

  Accordingly, in this metal protective film forming step, when the filament 15 is placed in a vacuum, a very small amount of deposits such as moisture existing on the surface of the filament 15 are evaporated and removed. As a result, the surface of the filament 15 is cleaned before the metal protective film 17 is formed. At this time, since the filament 15 is not heated, the tungsten constituting the filament 15 does not deteriorate.

  Thus, the metal protective film 17 is formed on the surface of the filament 15 once cleaned by ion plating, sputtering or vapor deposition. After the metal protective film 17 is formed on the surface of the filament 15 in the vacuum chamber, the vacuum chamber is returned to atmospheric pressure, and the filament assembly 11 is removed from the vacuum chamber.

  Thus, the filament 15 having the metal protective film 17 formed on the surface is provided in the filament assembly 11. Thereafter, the filament assembly 11 is attached to the electron gun 1. The electron gun 1 is mounted on an electron beam device.

After the electron gun 1 is mounted on the electron beam device, the inside of the electron gun 1 is evacuated, and then the filament 15 is heated by supplying a heating current to the filament 15, thereby aging the filament 15. The pressure inside the electron gun 15 at this time is 1 * 10 ⁻³ Pa or less. Further, a heating current is passed so that the tip of the filament 15 is around 2700 to 2800 ° C.

  At this time, the metal protective film 17 formed on the surface of the filament 15 is melted and evaporated. That is, the melting point of the metal protective film 17 is much lower than the heating temperature of the filament. Here, the melting point of gold constituting the metal protective film 17 in the present embodiment is 1063 ° C. As a result, the metal protective film 17 is removed from the surface of the filament 15. At the same time, a very small amount of adhering substances such as moisture adhering to the surface of the metal protective film 17 when the electron gun 1 is mounted on the electron beam apparatus also evaporates.

  As a result, the surface of the filament 15 is exposed during the aging, but the surface of the filament 15 has already been cleaned in the above-described metal protective film forming step, and the surface is attached with an adhering substance such as moisture. Does not remain.

  Therefore, even if the filament 15 is heated to a high temperature in a vacuum atmosphere in the aging process, the tungsten constituting the filament 15 does not deteriorate. Therefore, even if the filament 15 is continuously used after the aging process, the filament 15 is hardly broken and the life of the filament 15 is extended.

  Although the average life of the filament in the conventional example is 50 to 100 hours, in the present embodiment, as a result of the experiment, it has been confirmed that the average life of the filament is about 200 to 550 hours.

  Here, some of the experimental results are shown as examples below.

  A metal protective film made of gold was formed on the surface of the filament made of tungsten by an ion plating method. The lifetime of the filament at this time was 520 hours.

  A metal protective film made of gold was formed on the surface of the filament made of tungsten by vapor deposition. The lifetime of the filament at this time was 270 hours.

  As described above, in the present invention, the filament contains at least tungsten, and a metal protective film made of a metal that is melted and evaporated by heating under vacuum in which electrons are emitted is formed on the surface of the filament. Has been.

  Therefore, even if the electron gun with the filament attached is mounted on the electron beam apparatus and aging is performed, deposits such as moisture due to exposure to the atmosphere before the mounting are on the protective film formed on the filament surface. Therefore, the deposit is completely removed together with the evaporation of the protective film during the aging.

  Therefore, since the aging is performed in the state where there is no deposit such as moisture on the surface of the filament containing tungsten, it is possible to prevent the tungsten constituting the filament from being deteriorated, thereby prolonging the life of the filament. it can.

  In the above embodiment, the filament 15 is made of polycrystalline tungsten, but may be made of an alloy made of tungsten and rhenium (Re).

  Further, the metal protective film formed on the surface of the filament 15 may be made of platinum (Pt) or titanium (Ti) in addition to the above-described gold. Here, the melting point of platinum is 1774 ° C., and the melting point of titanium is 1725 ° C. These metals can also be formed on the surface of the filament 15 by ion plating, sputtering, or vapor deposition.

  Furthermore, in the said embodiment, although the filament 15 was an example of a hairpin filament, it is not restricted to this, For example, the thing of any form in a point filament, a sharped filament, and a semi point filament may be sufficient. .

  In the above embodiment, the electron gun 1 has been described as an example of a thermionic gun, but the present invention can also be applied to an example of a hot cathode field emission gun or a cold cathode field emission gun.

Here, in the example of the cold cathode field emission gun, after the cold cathode field emission gun (hereinafter referred to as an electron gun) is mounted on the electron beam apparatus, the inside of the electron gun is evacuated to perform aging. Is done. The pressure inside the electron gun at this time is 1 * 10 ⁻⁸ Pa or less. In this aging process, flushing is performed in which the filament of the electron gun is heated for several seconds. In this flushing, the filament is heated to 2000 to 3000 ° C. by passing a current of 2 to 3 A through the filament for 1 to 3 seconds.

  By performing this flushing, the metal protective film formed on the surface of the filament is melted and evaporated. At the same time, a very small amount of adhering matter such as moisture adhering to the surface of the metal protective film when the electron gun is mounted on the electron beam apparatus is also evaporated. Thereby, the effect similar to the above can be acquired.

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 this invention. It is a schematic block diagram which shows the front-end | tip part of the filament in 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 DESCRIPTION OF SYMBOLS 13 ... Stem pole, 14 ... Welding material, 15 ... Filament, 16 ... Filament tip part, 17 ... Metal protective film

Claims (7)

In a filament assembly comprising a filament that is heated under vacuum and emits electrons, the filament contains at least tungsten, and the metal protection that is melted and evaporated by heating under the vacuum and removed from the filament surface A filament assembly, wherein a film made of gold, platinum, or titanium is formed on the surface of the filament as the film . 2. The filament assembly according to claim 1, wherein the metal protective film is formed on the surface of the filament by ion plating, sputtering or vapor deposition. The metal protective film, filament assembly according to claim 1 or 2, characterized in that formed on the surface of the filaments at a film thickness of 10 to 1000 nm. The filament assembly according to any one of claims 1 to 3 , wherein the filament has one of a hairpin filament, a point filament, a sharped filament, and a semipoint filament. Claims 1 to 4 electron gun having a filament assembly according to any one. The electron gun according to claim 5, wherein the electron gun is a thermal electron gun. An electron beam apparatus comprising the electron gun according to claim 5 .

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