JPS5838905B2 - metal ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid metal ion source, and particularly to an ion source capable of generating a stable ion beam with a long life.

Ion beam exposure using metal ions such as gallium is attracting attention as an exposure method for producing sub-micron patterns because the diffusion of ions within the resist is smaller than exposure using electron beams. Research into metal ion sources is currently underway.

FIG. 1 shows an example of a liquid metal ion source, in which part 1 is a reservoir made of metal such as tantalum with pores 2 provided at the bottom. Contains gallium-3.

A needle-like member 4 made of tungsten is placed through the pore 2 at the bottom of the reservoir, and one end of the needle-like member is fixed to the side surface of the reservoir by spot welding, for example, and is made into a needle shape by electrolytic polishing. The other end is placed opposite the cathode 5 at ground potential.

A tungsten filament 6 is spot-welded to the reservoir 1 and a heating current is supplied to the filament 6 from a power source 7.

Furthermore, a positive high voltage is applied to the reservoir 1 and the needle member 4 from a power source 8.

Using the above-mentioned ion source, a strong electric field is applied to the tip of the needle-like member 4, and as a result, gallium inside the reservoir passes through the pore 2 at the bottom due to the strong electric field, and is deposited at the tip of the needle-like member 4. be drawn out.

The gallium at the tip forms a Taylor cone (
Forms a conical protrusion called Taylor Cone.

An electric field is concentrated at the tip of this conical protrusion, and gallium at the tip is evaporated by the electric field, ionized, and extracted as gallium ions.

Although such an ion source has very high brightness, it is difficult to generate a stable ion beam unless the temperature of the gallium is maintained at a certain temperature.

In other words, when the temperature of gallium is low, the transfer resistance of the path through which the surface of the needle member 4 is transferred toward the tip becomes high, and the flow of gallium subjected to field evaporation from the tip becomes unstable and discontinuous. This results in instability of the ion beam.

For this purpose, the filament 61/i is heated by supplying an electric current, and the reservoir 1,
The needle member 4 and gallium are heated so that gallium in the reservoir is stably and continuously transferred to the tip of the needle member.

In general, liquid metals such as gallium move across material surfaces by thermal diffusion, but this diffusion rate changes depending on the temperature, being faster at higher temperatures and slower as the temperature decreases.
Diffusion does not occur below a certain temperature.

Therefore, in the conventional ion source described above, the gallium in the reservoir 1 oozes out to the outer surface of the reservoir due to thermal diffusion and further moves on the surface of the filament 6.

One end of the filament 6 is fixed to a support 9, but the temperature of the filament portion close to the support 9 is low, and the diffusion rate of gallium is significantly reduced in this portion, so that the gallium metal is It stays and forms a lump 10.

This gallium on the surface of the filament, especially the lump 10, lowers the effective electrical resistance of the filament, and as a result, the heating temperature of the gallium in the reservoir becomes low, and the gallium in the reservoir is stably transferred to the tip of the needle-like member 4. As a result, a stable ion beam cannot be obtained.

Furthermore, gallium that migrates through the filament surface by thermal diffusion accelerates the consumption of gallium in the reservoir, shortening the life of the ion source.

The present invention has been made in view of the above-mentioned points, and includes: a reservoir portion that stores a metal to be ionized; a needle-like member having a needle-like tip portion to which liquid metal is supplied from the reservoir portion;
A means for forming a strong electric field in the needle-like tip, and a filament for heating the metal to be ionized by being thermally connected to the reservoir part or the needle-like member, the filament, the reservoir part, To provide a metal ion source capable of generating a stable ion beam with a long life by configuring so that at least a part of the surface of each needle member is covered with a substance having poor affinity with liquid metal. .

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

FIG. 2 shows an embodiment of the present invention, and in this embodiment, the same parts as those in FIG. 1 are given the same numbers and their explanation will be omitted.

A thin ceramic 11 is welded to the surface of the filament 6, which is spot welded to the reservoir 1 containing gallium 3, near the reservoir 1.

The ceramic has poor affinity with liquid metals such as gallium, and therefore, the liquid metal moving on the surface of the reservoir 10 by thermal diffusion is prevented from diffusing in the low temperature direction closer to the support 9 of the filament 6 by the ceramic 11. be done.

As a result, no lumps of liquid metal are formed in the filament 6, and therefore the effective electrical resistance of the filament does not decrease significantly, and the gallium 3 in the reservoir 1 can be heated to the desired temperature, allowing stable heating of the gallium 3 in the reservoir. Add gallium to the needle-like member 4
can be transferred to the tip of the

In addition, since the liquid metal does not diffuse on the surface of the filament 6 and no lumps of liquid metal occur, wasteful consumption of metal is eliminated and an ion source with a long life is provided.

In this embodiment, ceramic, which is a substance with poor affinity for gallium, is provided so as to partially cover the filament 6, but the entire surface of the filament 6 may be covered with ceramic. It is also preferable to weld ceramic □ to the surface of the reservoir 1 near the part to be welded to prevent the metal from diffusing into the filament 6.

FIG. 3 shows another embodiment of the present invention, in which a member 21 whose one end is needle-shaped has a coiled intermediate portion, which serves as a reservoir portion 22 for the liquid metal.

The other end of the needle-like member 21 is spot-welded to a filament 23, and a heating current is supplied to the filament 23.

As the filament is heated, the liquid metal stored in the needle member 21 and the coiled reservoir portion 22 is heated to a desired temperature, so that the liquid metal is stably supplied to the needle tip of the member 21.

A ceramic 24 is welded to the surface of the part of the member 21 that is close to the filament 23, and as a result, the heat diffusion of the liquid metal to the surface of the filament 23 is prevented by the ceramic 24.
Blocked by 4.

The present invention has been described in detail above, and since the ion source according to the present invention can prevent liquid metal from diffusing into the low-temperature portion of the filament, it is possible to generate a stable ion beam with a long life.

Note that the present invention is not limited to the embodiments described above, and can be modified in many ways.

For example, gallium was used as the metal to be ionized, but
The present invention can also be applied when a metal such as cesium is used as an ionized metal.

In addition to the type of ion source in which liquid metal is placed in the reservoir part, for example, a powdered substance such as a cesium compound is placed in the reservoir part, and by heating the substance, it is supplied in liquid form to the needle tip part. The present invention can also be applied to type ion sources.

Further, although ceramic is used as a substance having poor affinity with liquid metal, other substances such as glass or carbide can be used depending on the type of liquid metal.

[Brief explanation of drawings]

Figure 1 shows a conventional metal ion source, Figures 2 and 3
Each figure is a diagram showing an embodiment of the present invention. 1: Reservoir, 2: Pore, 3: Gallium, 4: Acicular member, 5: Cathode, 6: Filament, 7: Heating power source, 8: High voltage power source, 9: Support, 10: Mass, 11: Ceramic .

Claims (1)

[Scope of Claims] 1. A reservoir portion that stores a metal to be ionized, a needle-like member having a needle-like tip portion to which liquid metal is supplied from the reservoir portion, and a strong electric field formed in the needle-like tip portion. and a filament for heating the metal to be ionized by being thermally connected to the reservoir portion or the needle-like member, and at least one of the filament, the reservoir portion, and the needle-like member. A metal ion source whose surface is covered with a substance that has poor affinity for liquid metals. 2. The metal ion source according to claim 1, wherein the reservoir portion is a container having a pore in its lower part, and the needle-like member is disposed through the pore. 3. The metal ion source according to claim 1, wherein a part of the needle-like member serves as a reservoir portion that holds the metal to be ionized.