JPH0778552A - Field emission type cathode and manufacture thereof - Google Patents

Abstract

PURPOSE:To actuate a field emission type cathode for a long time stably by applying metal powder having a higher melting point than a specific temperature on a joint part of a single crystal wire with a heating filament, and sintering the metal powder for supporting the joint part. CONSTITUTION:On a joint part of a high melting point metal single wire 1 of tungsten or the like with a filament 2, metal powder 3 of zirconium or the like having a melting point which is lower than the melting point of the wire 1 and the filament 2 and which is 1800K or more is applied. This is then heated and sintered to harden the powder 3. The single crystal wire 1 and the filament 2 are thus joined together, and conductivity is provided. Generation of defects such as those in spot welding will not occur in the single crystal wire 1, thereby current stability, service life, and reliability of a cathode are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron source used in an electron beam application apparatus such as an electron beam drawing apparatus and an electron microscope, and more particularly to a long-life and stable field emission type cathode and its manufacturing method.

[0002]

2. Description of the Related Art A field emission type cathode, which is widely used as an electron source for electron beam application devices such as electron beam drawing devices and electron microscopes, has a single crystal wire of a thin refractory metal whose tip is needle-shaped. , A specific plane orientation where the tip has a low work function, for example,
The (100) plane and the (310) plane are formed, and a strong electric field is applied to the plane to pull out electrons by the tunnel effect. About this, page 141 of the Electron / Ion Beam Handbook
Pp. 159. This field emission cathode consists of a hairpin-shaped filament for heating and a thin single-melting-point metal single-crystal wire with a needle-shaped tip for drawing out electrons, but the junction is a spot. It is done by welding. However, the spot welding causes defects in the crystal arrangement of the single crystal lines.

There are two types of field emission cathodes, one that is used at room temperature and one that is used at high temperature. In the former, in order to remove unnecessary gas molecules attached to the needle-shaped tip, 1800
Flushing for heating for several seconds at a temperature of ℃ or more is performed for more than ten hours to once a day. The latter is used while being heated at a temperature of 1300 ° C or higher. By these heatings, crystal defects generated during spot welding grow in the direction of the tip of the single crystal. When this defect reaches the tip due to long-term use, the crystal orientation of the tip changes, causing axial misalignment in the electron emission direction or no electron emission.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a method for manufacturing a field emission type cathode which does not cause a defect in the crystal arrangement of a single crystal even if it is used for a long time. To provide a mold cathode.

[0005]

[Means for Solving the Problems] A heating filament constituting a field emission type cathode and a single crystal wire of a thin refractory metal having a needle-like tip for drawing out an electron are joined.
The above problems can be achieved by applying and sintering a metal powder or a carbon material.

[0006]

FIG. 1 (a) is an explanatory view of the field emission type cathode of the present invention.
Shown in. 1 is a refractory metal single crystal line. 2 is a hairpin-shaped filament composed of a polycrystalline wire of a refractory metal. 4 is a terminal made of stainless steel or the like, and the filament 2 is spot-welded. 5 is a ceramic insulator. Refractory metal single crystal wire 1
The refractory metal single crystal wire 1
A metal powder or a carbon material 3 having a lower melting point than the filament 2 is applied. By heating and sintering this, the metal powder or the carbon material 3 is hardened. As a result, the high melting point metal single crystal wire 1 and the filament 2 are joined, and conductivity is also obtained. Here, the difference from the conventional spot welding is that the single crystal wire 1 of high melting point metal and the filament 2
It means that the crystal structure of is not burdened at all. Therefore, no defects occur in the refractory metal single crystal wire 1, so that the above problems can be solved, and the current stability, life, and reliability of the cathode can be significantly improved.

[0007]

EXAMPLE The structure and manufacturing method of the field emission type cathode according to the present invention will be described with reference to FIG. As a first embodiment, a material using tungsten as a material for forming a field emission cathode will be described. A tungsten polycrystal wire having a diameter of 0.15 mm was molded into a hairpin shape for heating to form a filament 2, and the plane orientation (10
The tungsten single crystal 1 of 0) was joined using zirconium powder. In order to use zirconium powder for joining, first, zirconium powder (particle size: about 0.1 μm) is dissolved in a viscous liquid obtained by dissolving nitrocellulose in butyl acetate, and applied to the joint between the tungsten single crystal 1 and the filament 2. To do. After this is naturally dried and cured, it is heated and sintered in a vacuum. At this time, while confirming the heating temperature with a radiation thermometer, the temperature is slowly increased to 1700 ° C., which is about 100 ° C. lower than the melting point of zirconium. By performing this sintering, the tungsten single crystal 1 and the filament 2 are joined, and conductivity is obtained.

Next, by utilizing this conductivity, electric field polishing for sharpening the tip of the tungsten single crystal 1 into a needle shape is performed. The purpose of this electric field polishing is to dip the tungsten single crystal 1 in an aqueous NaOH solution and apply a direct current voltage to gradually cut the tungsten single crystal 1 so that the tungsten single crystal 1 is cut. Crystal 1 with a tip radius of curvature of about 0.1 μm is completed. A diffusion agent 6 for lowering the work function of the tip of the tungsten single crystal 1 is added to the field emission type cathode thus produced.
As shown in FIG.
It is applied onto the zirconium powder 3 as shown in (b).

FIG. 2 shows an arrangement for putting the thus-fabricated field emission type cathode into a vacuum container and drawing out electrons.
A heating power supply 7 for heating the field emission type cathode 12, a high voltage power supply 8 for applying a strong electric field between the extraction electrode 9 and the field emission type cathode 12, and a beam current extracted from the field emission type cathode 12 are detected. Faraday gauge 10 to do
And an ammeter 11 for measuring the current. Using this device, the electron emission characteristics of the field emission type cathode invented this time and the conventional type were compared.

The evaluation experiment procedure is shown below. First, the filament 2 was electrically heated by the heating power source 7 to sinter the zirconium oxide powder. At this time, the temperature was slowly raised to 1430 ° C. over about 30 minutes. After that, a high voltage was gradually applied by the extraction power source 8, and at about 4 kV, an electron emission pattern appeared on the extraction electrode 9 coated with the phosphor. When the current detected by the Faraday gauge 10 through the small hole of the extraction electrode 9 at this time was measured, it was possible to obtain an electron emission characteristic equivalent to that of the conventional type.
It was also confirmed that the axis of the electron emission surface was stable for not less than 5000 hours and was stable. Further, the field emission cathode using the plane orientation (310) of the tungsten single crystal 1 without using a diffusing agent was subjected to flashing at 1800 ° C. or more 1000 times or more while being used at room temperature. Did not happen.

Although the case where zirconium is used as the metal for joining the tungsten single crystal 1 and the filament 2 has been described above, the same result can be obtained by using a metal powder such as titanium, hafnium, yttrium, scandium, thorium or beryllium. was gotten. Further, although a liquid prepared by dissolving nitrocellulose in butyl acetate was used for the dissolution, the present invention is not limited to this, and an organic solvent or pure water may be used.

Next, as a second embodiment, a description will be given of using glassy carbon instead of metal powder for joining the tungsten single crystal 1 and the filament 2. The glassy carbon used at this time was prepared by mixing furfuryl alcohol and ethyl P-toluenesulfonate, and heating the furan resin obtained by stirring in a constant temperature bath for 2 days to carbonize it. In the case of joining by means of glassy carbon, a furan resin in a mucous state is applied to the joint between the tungsten single crystal 1 and the filament 2 as shown in FIG. 1 (a), and heated to 1200 ° C. in vacuum. By this heating, the furan resin is carbonized to form glassy carbon and conductivity is obtained. When a diffusing agent was applied to the thus-fabricated field emission type cathode by a coating method as shown in FIG. 1 (b), the same electron emission characteristics as those of the conventional type could be obtained, and the electron emission surface of the electron emission surface of 5000 hours or more It was also confirmed that the axis was stable without shifting. Further, as described in the first embodiment, a field emission type cathode having a plane orientation (310) of the tungsten single crystal 1 which does not use a diffusing agent was manufactured, and flushing at 1800 ° C. or more was performed 1000 times or more. No axis deviation of electron emission occurred.

As described above, the heating temperature and the extraction voltage described in the present embodiment are merely examples, and they can be used without being limited to these numerical values depending on the coating material of the joint and other conditions.

Further, although tungsten is used as the material of the field emission type cathode in the above embodiments, both single crystal and polycrystal may be high melting point metals. Similar to tungsten, molybdenum, tantalum, and rhenium having a melting point of 2500 ° C. or higher gave the same results as when tungsten was used. Therefore, the melting point is 2500
Any metal material having a temperature of ℃ or more can be used without being particular about these. Similar results were obtained with oxides of titanium, hafnium, yttrium, scandium, thorium, beryllium, etc. as well as zirconium oxide as the diffusing agent. In addition, the application place of the diffusing agent is not at the joint between the tungsten single crystal 1 and the filament 2, but as shown in FIG.
As shown in (c), the same applies when applied to the middle part of the tungsten single crystal 1.

[0015]

According to the present invention, a field emission type cathode can be manufactured without using spot welding, and a crystal defect does not occur in a single crystal. Therefore, it is possible to realize a field emission cathode that is stable and has a long life even in a high temperature range.

[Brief description of drawings]

FIG. 1 is an explanatory view of a field emission type cathode of the present invention.

FIG. 2 is a circuit diagram of a characteristic evaluation system of the present field emission cathode.

[Explanation of symbols]

1 ... Single crystal, 2 ... Filament, 3 ... Refractory metal powder or carbon material, 4 ... Terminal, 5 ... Ceramic insulator or glass base, 6 ... Diffusing agent.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiro Kuroda 1-280, Higashi Koikekubo, Kokubunji, Tokyo Metropolitan Research Center, Hitachi Ltd.

Claims (4)

[Claims] 1. A field emission type cathode comprising a single crystal wire of a high melting point metal having a pointed needle-like tip and a heating filament in which a polycrystalline thin wire of a high melting point metal is formed in a hairpin shape.
A structure in which a metal powder having a melting point of 1800 K or more is applied to a joint portion between the single crystal wire and the heating filament, and the joint portion between the single crystal wire and the heating filament is supported by sintering the metal powder. A field emission cathode. 2. A field emission type cathode comprising a single crystal wire of a high melting point metal having a pointed needle-like tip and a heating filament in which a polycrystalline thin wire of a high melting point metal is formed in a hairpin shape.
A field emission type cathode characterized in that a carbon material is applied to a joint portion between the single crystal wire and the heating filament, and the joint portion between the single crystal wire and the heating filament is supported by sintering thereof. 3. The metal powder according to claim 1, which is applied to a joint portion between the single crystal wire and the heating filament,
A method for producing a field emission cathode, which is applied as a paste with pure water or an organic solvent. 4. The oxide of a metal having a low work function or electronegativity is added to pure metal or organic at the metal powder sintered joint between the single crystal wire and the heating filament according to claim 1, 2, or 3. A method for producing a field emission cathode, which is applied as a paste with a solvent.