JPS6059623A - Liquid metal ion source - Google Patents

Abstract

PURPOSE:To lengthen a life of a liquid metal ion source loaded with a liquid metal having strong reaction or a liquid metal having a high melting point by using an emitter metal wire rod on whose surface a metal carbide layer is formed. CONSTITUTION:Firstly, two tantalum wires 1 and 5 are spot-welded with a hair pin 3 of a tantalum wire while forming a needle by making the tip of the tantalum wire 1 into a needle shape by electrolytic polishing. Secondly, by performing washing and shaping as well as a carbonizing reaction, a carbonized tantalum layer is formed on the surface of the tantalum emitter metal wire rod, while the needle tip part subject to the severest wear becomes a carbonized tantalum single crystal. This is loaded with the liquid metal 4 while being made into an ion source. As a molding process is performed to the emitter metal wire rod before carbonization, its shape can be freely selected. Further, a single crystal carbide of good quality can be formed at the needle tip part subject to the severest wear.

Description

[Detailed description of the invention] Regarding liquid metal ion sources, especially those with high melting points.

The aim is to enable a liquid metal ion source equipped with a highly reactive liquid metal to emit ions stably over a long period of time.

Since liquid metal ion sources can easily produce high-intensity, micro-diameter ion beams, they can be applied to microfabrication techniques such as maskless ion implantation, ion beam etching, and thin film production in electronic device manufacturing. It is expected. A liquid metal ion source is made by electrolytically polishing a fine wire (about 0.2 mm in diameter) of a heat-resistant metal that forms the emitter metal wire into a needle shape with a tip radius of several μm, and then coating the surface with liquid metal. The liquid metal is wetted with water, and a strong electric field applied to the tip ionizes the liquid metal.

The type of liquid metal loaded in the liquid metal ion source is selected depending on the intended use of the liquid metal ion source.

In particular, when the reactivity of the liquid metal is strong or when the melting point of the liquid metal is high, the reaction between the liquid metal and the emitter metal wire progresses easily, resulting in significant wear of the emitter metal wire, especially the needle part. .

The disadvantage is that the life of the liquid metal ion source is shortened.

An example of a highly reactive material is aluminum (AZ).
A liquid metal consisting of Liquid metal ion sources made of aluminum are important for manufacturing new electronic devices and for ion beam deposition, but ordinary liquid metal ion sources that use tungsten (W) as the emitter metal wire have a lifespan of several seconds. It takes about an hour and is not practical. Unfortunately, since the emitter metal wire is eluted into the liquid metal, the elements that make up the emitter metal wire are also ionized, causing a decrease in the purity of the emitted ions. In addition, yJe (B) and silicon (Si) are important elements in the production of electronic devices, and examples of elements with high melting points include yJe (B) and silicon (Si). These are platinum (pt)-boron (
B), nickel (Ni)-boron (B), gold (A,)
-It is used as a eutectic alloy such as silicon (Si) to lower its melting point. These liquid metal ion sources are.

Ron ions or self ions are used for doping.
Although it is expected to be used as an ion source for extracting silicon from mother ivy, even if the melting point is lowered as described above, ordinary liquid metals such as those using tungsten as the emitter metal wire Ion sources have extremely short lifetimes and are not suitable for practical use.

In addition to tungsten, the emitter metal wire materials include tantalum (Ta), molybdenum (Mo), and titanium (Ti).
It is also possible to use heat-resistant metals such as , zirconium (Zr), vanadium (V), or niobium (Nb), but these also have the same drawback of short life as when tungsten is used as the emitter metal wire. There is.

The purpose of the present invention is to eliminate the above-mentioned drawbacks and to achieve a longer life of a liquid metal ion source equipped with a highly reactive liquid metal or a high melting point liquid metal (F:).

According to the present invention, there is obtained a liquid metal ion source in which a liquid metal is mounted on an emitter metal wire, which is characterized by using an emitter metal wire having a metal carbide layer formed on its surface.

Next, embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 1, a liquid metal ion source according to an embodiment of the present invention includes a liquid metal 4 mounted on emitter metal wires 1, 3, and 5 having tantalum carbide (TaC) formed on their surfaces. Here, ■ is a needle, 3 is a hairpin type heater, and 5 is a horizontal bar.

2 is a metal reservoir.

Electron-emitting emitters having a metal carbide layer formed on their surfaces (used as electron beam sources for electron beam application equipment such as electron microscopes) are disclosed in Japanese Patent Publication No. 56-31046, Japanese Patent Publication No. 56-31047, and Japanese Patent Publication No. 56-31047. Kaisho 54-1349
It is disclosed in Publication No. 64.

In the present invention, a metal wire having a metal carbide layer formed on its surface is used as a metal wire for an emitter whose purpose is not to emit electrons but to emit ions. Even in the present invention.

Metal carbide can be formed on the surface of the emitter metal wire by substantially the same treatment as the metal carbide of the electron-emitting emitter described above.

The emitter metal wire shown in FIG. 1(4) having tantalum carbide (TaC) formed on its surface is prepared in the following manner. That is, first, two tantalum wires (one corresponding to king, one corresponding to king,
An emitter metal wire is formed by spot welding the tantalum wire (corresponding to No. 5) and forming a needle by making the tip of the tantalum wire (corresponding to No. 1) into a needle shape by electropolishing. Next, this emitter metal wire is I
In a vacuum of less than Torr, flushing is performed while observing a field emission (FE) pattern to clean and shape the surface of the emitter metal wire. Next, in this state, ethylene (C2H4) r hydrogen (H
2), argon (Ar) at 1 (1,200,
200 Torr was introduced, and the emitter metal wire was heated to about 23 Torr.
When a carbonization reaction is carried out by heating with electricity for 15 seconds at 00° C., a tantalum carbide layer is formed on the surface of the tantalum emitter metal wire, and the tip of the needle, which is most consumed, becomes a mental carbide (TaC) single crystal.

It is difficult to mold the conventional hard and brittle carbide RL' into a tip shape with a tip shape suitable for ion radiation, such as crystals or whiskers, and the process may require several steps to be formed on the support. However, in the present invention, since the forming process is performed on the emitter metal wire before carbonization, the shape can be freely selected. Furthermore, high-quality single crystal carbide can be formed at the tip of the 1 to 21 dollar tip, which is the most consumed.

The above example is an example of carbonization by electrical heating.

If this carbonization reaction is carried out using laser light, infrared rays, etc., it is possible to carbonize emitter metal wires (especially needles) of other shapes of ion sources for which current heating cannot be used. Emitter metal wire for ion sources of all shapes (4
? metal carbide can be formed on the surface of the needle).

If such an emitter metal wire with metal carbide formed on two surfaces is used, a stable ion source with a long life can be produced because the metal carbide has the following properties.

l) High melting point. (3500°C to 42oo°C) 2) High hardness and high mechanical strength at high temperatures.

3) Strong resistance to residual gas.

4) High electrical and thermal conductivity, comparable to metal 2 alloys.

In addition to the above-mentioned tantalum, tungsten (W) may be used as the emitter metal wire. Molybdenum (Mo).

Titanium (Ti), zirconium (Zr), nocnasium (V), or niobium (Nb) can also be used as a transition metal of group 1 to 2, and a metal carbide layer is formed on the emitter metal wire by the same method as above. It is possible to form.

The emitter metal spheroid produced by the above method and having a metal carbide layer formed on its surface is already in the form of a needle with a tip radius of several μtn suitable for ion emission at the stage of tantalum (Ta). In order to mount liquid metal on this, first,
The emitter metal wire shown in Figure (A) is placed in a vacuum chamber, and the heater, ie, the filament 3, is energized and heated to generate gas and clean the surface. Next, the emitter wire section is immersed in a liquid metal crucible placed in the same vacuum chamber, and when a sufficient amount of the emitter wire is deposited, liquid metal 4 is deposited in the metal reservoir 2 as shown in FIG. 1(B). It is in a mounted form. In this state, when a high voltage of several kV to IOkV is applied to the counter electrode installed in the same hole, the electric field promotes the surface diffusion of the liquid metal 4 and wetting the needle. The wetting progresses toward the tip, and the wetting becomes uniform, resulting in a completed shape as shown in FIG. 1(C).

A liquid metal ion source using an emitter metal wire with a metal carbide layer formed on its surface by such a method has the following advantages over a normal liquid metal ion source that does not form a metal carbide layer. 0 (1) Strong resistance of metal carbides, aluminum (A
It is very stable even with highly reactive liquid metals such as I-), and the substance constituting the emitter metal wire does not dissolve into the liquid metal. For this reason, the life of the liquid metal ion source can be extended. FIG. 2 shows the mass spectrometer of the At ion source produced in this way measured by a single focusing magnetic field type mass spectrometer, and no ion emission due to elution of the emitter wire (Ta) was observed.

(2) Metal carbides are substances with very high melting points (
3,400 to 4,200°C), thereby extending the life of a liquid metal ion source with a high melting point.

In the above embodiments, the emitter metal wire of tank carbide (TaC) was explained. However, it goes without saying that the present invention is not limited to these embodiments, and also includes modifications to the embodiments.

As explained above, according to the present invention, it is possible to extend the life of a liquid metal ion source equipped with a highly reactive liquid metal or a liquid metal with a high melting point.

[Brief explanation of the drawing]

FIGS. 1(A), 1(B), and 1(C) are front views showing a liquid metal ion source according to an embodiment of the present invention in the order of the manufacturing process. Figure 2 shows an aluminum (At) liquid gold mass wave reactor according to an embodiment of the present invention using an emitter metal wire with tantalum carbide (TaC) formed on the surface. This is a diagram. In the figure, ] indicates a needle, 2 indicates a metal reservoir, 3 indicates a heater, 4 indicates liquid metal, and 5 indicates horizontal/(-.

Claims (1)

[Claims] A liquid metal ion source in which a liquid metal is mounted on an emitter metal wire, characterized in that the emitter metal wire has a metal carbide layer formed on its surface.