JPS5835829A - Metal ion source - Google Patents

Abstract

PURPOSE:To generate an ion beam of a long life and stability by a method wherein a holding member thermally connected with a reservoir and a needle- shaped member as well electrically heated is formed with a substance having poor affinity with a liquid metal to prevent needless diffusion of the liquid metal. CONSTITUTION:When a heating current is applied to between the stays 12 and 13, the graphite 20 and 21 is heated by electrification to rise to about 400 deg.K- 600 deg.K in temperature. The heat in the graphite 20 and 21 transfers to a needle- shaped member 25 and gallium 22 while gallium in a reservoir transfers stably and continuously to a tip of the needle-shaped member 25. Gallium exudes to an outer surface of the reservoir 23 through thermal diffusion but does not diffuse on a surface of graphite because of its poor affinity with graphite 20 and 21. Accordingly graphite 20 and 21 is always heated up to the required temperature so as to enable to transfer gallium to the tip of the needle-shaped member 25 stably for hours.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid metal ion source, and particularly relates to an ion source that can generate a stable ion beam with a long lifespan. Because the diffusion of ions is smaller than exposure using an electron beam, it is attracting attention as an exposure method for producing submicron or smaller patterns, and for this reason, research into metal ion sources is progressing in various fields. Figure 1 shows an example of a liquid metal ion source, in which 1 is a reservoir made of metal such as tantalum with pores 2 in the bottom 1, and a WL main body inside the reservoir 1. A gold metal such as gallium 6 is placed in the reservoir (a needle-like member 4 made of tungsten is placed through the pore 2 at the bottom, and one end of the needle-like member is attached to the side surface of the reservoir). It is fixed by welding, and the other end, which has been electropolished into a needle shape, is placed opposite the cathode 5 at ground potential.

A tungsten filament 6 is spot-welded to the reservoir 11, and a heating current is supplied to the filament 6 from a power source 7. A positive high voltage is applied to the needle member 41 from the power source 8.

In 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 reaches the tip of the needle-like member 4. be drawn out. The gallium at the tip forms a circular protrusion with a strong electric field, hence the name Taylor's cone. The electric field is concentrated at the tip of the conical protrusion, and the gallium at the tip is evaporated by the electric field and extracted as gallium ions. Although such an ion source has very high tC brightness, it is difficult to generate a stable ion beam unless the gallium temperature is maintained at a certain temperature.In other words, if the gallium temperature is low, the needle-like member 4 The transport resistance of the path through which the surface of the ion beam is directed toward the tip increases, and the flow of gallium that is subjected to field evaporation from the tip becomes unstable and discontinuous, resulting in instability of the ion beam. There is one thing. Therefore filament 6+
c [supply flow and heat, jl! 1. Due to the conductive heat iζ from the filament 6, the reservoir 1, the needle-shaped member 4. The gallium is heated and strained so that the gallium in the reservoir is continuously and stably transferred to the tip s1 of the needle-like member.

Now, in general, liquid metals such as gallium move on the surface of a material by thermal expansion, but this diffusion rate changes depending on the temperature, it is fast at high temperatures, slows down as the temperature decreases, and below a certain temperature, the diffusion rate changes depending on the temperature. No diffusion occurs. Therefore, in the conventional ion source mentioned above, the gallium in the reservoir 1 oozes out from the outer surface of the reservoir 1 due to the thermal expansion and further moves on the surface of the filament 6. Although one end of the filament 5 is fixed to the support 91, the temperature of the portion of the filament close to the support 9 is low, and the diffusion rate of gallium decreases significantly in this portion, causing gallium metal to remain. 0 to form 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 11 of the gallium in the reservoir becomes low (and the gallium in the reservoir is stably transferred to the tip of the needle member 4). (As a result, a stable ion beam cannot be obtained.Furthermore, the gallium that moves on the filament surface due to thermal diffusion 1 accelerates the dissipation of gallium in the reservoir, shortening the life of the ion source.

The present invention has been made in view of the above points, and includes: a reservoir section for storing a metal to be ionized; a needle-like member having a needle-like tip section to which liquid metal is supplied from the reservoir section;
means for forming a strong electric field at the tip of the scissors needle, and a means for forming a strong electric field at the tip of the scissor needle, and a through IE base ζ thermally connected to the reservoir part or the cough needle member.
Therefore, the metal ion source is equipped with a support member that generates heat, and the support member is made of a substance that has a low affinity with the liquid metal, and is capable of generating a stable ion beam over a short lifetime. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. One connected conductive strut 12 and 16 is attached. The tips of each of the pillars 12 and 16 are divided into five parts, including support parts 12a and 161 and movable parts 12b and 15b, respectively.
One ends of band-shaped elastic bodies 14 and 15 are fixed to a and 15 m with screws 16 and 17, respectively. The elastic body 14
．． The other end of 15 is made of a material with low thermal conductivity, such as insulator 1.
One end of 13.19 is in contact with the insulator 18.19.
Each support 512 m.

16a is movably passed through the shell, and the other end is the movable part 12
b, I is in contact with Ab. As a result, the movable portion 12b.

The tab is pressed inward by the elastic force of the elastic bodies 14 and 15. Of the movable parts 12b and 15b, 11111 is filled with liquid metal,
For example, a tantalum or tungsten reservoir 26 containing gallium 22 is arranged. A pore 24 is provided at the bottom of the reservoir 26 .
A needle-like member 25 made of tungsten, one end of which is spot-welded to side-1 of the reservoir 25, is disposed through the reservoir 25.

The needle-like tip of the member 25 is placed opposite a cathode (not shown).

In the configuration as described above, the reservoir 25 and the graphite 20, 21 are supported by the support 12.15 due to the pressing force lζ of the elastic body 14.15! This is retained. Here, the two pillars 12
If a heating current is supplied between and 16, graphite 20
, 21 is heated by electricity to 400 K to 600 K
Raise the temperature to ＠ degrees. The heat of the graph eye 1-20.21 is transferred to the needle member 25.21 through the reservoir 2S. As a result, the gallium in the reservoir is stably and continuously transferred to the tip of the needle-like member 25. Here, the heated gallium oozes out to the outer surface of the reservoir 25 due to thermal diffusion 1, but since the scissors graphite 20 and 21 have a confusing affinity with gallium, the gallium is not spread on the surface of the graphite due to the spreading koji Δ. do not have. Therefore, since the desired side 1 of graph eye) 20.21 is constantly heated by fζ energization iζ, the gallium 7 can be stably transferred to the tip of the needle member 25 for a long time, and stable ion 0 beam is obtained
In addition, since gallium does not diffuse from the graphite surface toward the support column 12.15, there is no wasteful consumption of straight metal.
A long-life ion source is provided.

Figure 5IN3 shows another embodiment of the invention, in which the middle part of a member 61 with one end cut into a needle shape is coiled, and this part serves as a reservoir part 6 of liquid metal such as gallium.
It becomes 2. Although not shown, the needle-like member 51 is suppressed and held by the graphite supports 12, 16+ as shown in the embodiment of FIG. 2, and a heating current is supplied to the graphites 20, 21. is configured to be

Also in this Example 1ζ, the liquid metal that thermally diffuses on the surface of the needle member 61 does not diffuse on the graphite surface, so a stable ion source with a long life is provided.

The present invention has been described in detail above, and since the ion source based on the present invention 1 can prevent unnecessary diffusion of liquid metal,
Able to generate a stable ion beam with long life.
It should be noted that the present invention is not limited to the above-mentioned implementation capabilities and can be modified in many ways. Although gallium is used as the ionized metal, the present invention can also be applied to cases where a similar metal such as cesium is used as the ionized metal. In addition to the ion source in which a liquid metal is placed in the reservoir, a powdered substance such as a cesium compound is placed in the reservoir, and by heating the substance, it is supplied to the needle-like tip as a liquid. The present invention can also be applied to other ion sources. Furthermore, although graphite was used as the exothermic substance that has poor affinity with liquid metals, carbides such as silicon carbide or other substances that have poor affinity with liquid metals may also be used.

[Brief explanation of drawings]

Figure 5 shows a conventional metal ion source, Figures 2 and 3.
Each figure shows an embodiment of the present invention. Power source, 9: Support, 10: Mass, 11: Base, 12.
15: Post, 12g, 15m: Support part, 12b, lb:
Movable part, 14. Is dielastic body, 16.17=bis, 18
, 19: insulator, 20, 21: graphite, 22: gallium, 26: reservoir, 24: pore, 25: needle-like member. Patent Applicant JEOL Ltd. Representative Tadao Kase 2nd Row 13:

Claims (1)

[Scope of Claims] L: A reservoir section for storing metal to be ionized, a needle-like member having a needle-like tip section to which liquid metal is supplied from the reservoir section, and forming a strong electric field in the needle-like tip section. and a support member that is thermally connected and generates heat when energized, and the support member is made of a substance that has poor affinity with the liquid metal. A metal ion source 〇λ, characterized in that the reservoir portion is a container having a pore at the bottom, and the acicular member is disposed through the pores of the metal ion source according to claim 1. ion source. & 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. The fe-based metal ion source according to any one of claims 1, 2 and 3, wherein the support member is made of graphite. a The metal ion source O according to any one of claims 1, 2 and 3, wherein the support member is formed of a carbide.