JPH02812B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a field ionization liquid metal ion source.
Hydrodynamic ion source (hereinafter abbreviated as EHD ion source).

[Background of the invention]

The EHD ion source applies a strong electric field (several tens of kV) to the tip of a needle-shaped metal emitter covered in liquid metal.
When the electric field reaches a certain critical value, the electrostatic force applied to the liquid surface exceeds the contraction force due to surface tension, and it assumes a conical shape called a Taylor cone.At the same time, at the tip of this cone, the evaporation electric field of the liquid metal Strength is reached and ion release begins. This is the principle of the EHD ion source.

In recent years, as semiconductors have become more highly integrated, microfabrication using ion beams has been attracting attention. When performing microfabrication, it is necessary to reduce the spot diameter of the ion beam, but this necessarily involves a reduction in the ion beam current. The parameters governing the ion beam current irradiated onto the sample surface to be processed are the current density and the lateral kinetic energy component of the ions, so a high-intensity ion source with a small current emission surface and high current density is recommended as an ion source. things are required. In response to this requirement, a field emitter type (field ionization type) ion source has been devised. In particular, the EHD ion source has a high brightness of more than 10 ⁶ A/cm ² ·Sr and an energy half-width of less than 10 eV, making it possible to obtain a minutely focused ion beam.
On the other hand, since the liquid ionized metal is supplied along the surface of the needle tip to the tip, evaporation of the ionized metal around the ion source cannot be ignored. Therefore, the ionized metals are mainly Ga, In,
Low vapor pressure materials such as Au, Bi, Pb, Li, B, Cs, and Al are used. For example, PD Prewett et al. Journal of Physics Day 13 (1980) pp. 1747-55 (J.
Phys.D, 13 (1980) 1747-55).

The most common conventional EHD ion source is shown in Figure 1a.
As shown in the figure, a needle-like ion emitter 1 with a curvature of 1 to 2 μm at the tip is welded to the tip of a hairpin-shaped emitter wire 2, and an ionized metal 3 is mounted at the joint between the two. In order to further extend the lifespan, as shown in FIG. The structure is such that an ionized metal 3 is mounted between an auxiliary wire 4 provided at the center and a connecting portion between the ion emitter 1 and the hairpin-shaped emitter wire 2.

The materials of the ion emitter 1 and emitter wire 2 used in such an EHD ion source must have good wettability with the ionized metal mounted and must not cause any reaction. Therefore, for example, when the ionized metal is Ga, In, Au, or an alkali metal, a W wire is used, and when the ionized metal is Bi, a Ni-Cr wire is used.

In such conventional EHD ion sources, ionized metals are loaded in the following manner. That is, the tips of the ion emitter 1 and the emitter wire 2 are immersed in a pool of molten ionized metal, and then pulled up to solidify the ionized metal around the ion emitter 1, or in the case of Ga, etc., a syringe is used. Accordingly, there is a method of mounting the ionized metal 3 around the ion emitter 1. In the operating condition of the EHD ion source,
In order to uniformly wet the ion emitter 1, the ion emitter 1 is used while being heated to a temperature at which evaporation of the ionized metal and reaction with the emitter beam do not become a problem. The appropriate heating temperature is 600 to 700°C for Ga and approximately 1200°C for Au.

As mentioned above, with the conventional EHD ion source, it is easy to load ionized metal, but it is difficult to control the amount of loaded ionized metal, and the needle-like tip of the ion emitter 1 is difficult to control while loading the ionized metal. It has drawbacks such as being easily damaged and having a large amount of evaporation because the ionized metal is exposed.

[Object of the invention] The present invention is a diffusion replenishment type that compensates for the above-mentioned drawbacks.
This is an EHD ion source with a structure consisting of an ion emitter with a needle-like tip and a porous heating element containing ionized metal.

[Summary of the invention, Examples]

That is, as shown in FIG. 2, the ionized metal is contained in a porous heating element 2', to which an ion emitter 1 having a needle-like tip is attached. Note that FIG. 1A shows the porous heating element 2' having a hairpin shape, and FIG. The material of the porous heating element 2' may be any high-resistance material that does not easily react with ionized metals, and any one of W, Mo, Re, Ta, Ni, or an alloy thereof may be used. Regarding the case where the porous heating element 2' is manufactured using W as a material, W with a diameter of 5 to 20 μm and a length of 10 to 20 cm is used.
Make a bundle of twisted fibers and heat 1000 in _H2
℃ for 1 hour to remove the oxide film and carbon film on the surface, and perform preliminary sintering. Next, heat treatment is performed at 1600-1900℃ for 1-2 hours in vacuum or _H2 ,
Perform main sintering of the W fiber. By the above treatment, a porous body of W having a porosity of 20 to 40% is obtained.
The diameter of this porous body is the number of W fibers used,
It can be arbitrarily controlled by the heat treatment conditions for main sintering. Further, if necessary, the porosity can be easily adjusted by drawing the porous body after main sintering. That is, the porosity can be changed depending on the degree of wire drawing. Note that porous bodies can be manufactured using other metals in the same manner as described above.

Next, for example, a wire made of a porous material with a diameter of 0.15 mm is made, and the wire made of this porous material is cut to an appropriate length, and the hairpin-shaped porous heating element 2' shown in FIG. Make a coiled porous heating element 2',
This is immersed in a melt of ionized metal, or a wire or powder of ionized metal is attached around the porous heating element 2', and the porous heating element 2' is heat-treated in vacuum or in _H2 . By infiltrating the ionized metal into the pores, a porous heating element 2' containing the ionized metal is completed. Next, a wire for an ion emitter, for example, a W wire, is welded to the tip of this porous heating element 2', and the tip is etched with an etching solution such as a caustic soda aqueous solution to form a needle-shaped ion emitter with a radius of curvature of 1 to 2 μm. Make 1.

The diffusion replenishment type EHD ion source of the present invention is constructed as described above, and by heating the porous heating element 2' with electricity, the ionized metal contained in the pores is transferred to the acicular tip of the ion emitter 1. Diffusion replenishment can be performed at the tip.

An example of a diffusion replenishment type EHD ion source of the present invention with a further extended life is shown in FIG. 2c, as shown in FIG. During operation, ionized metal is diffused and supplied from the melt reservoir 5 to the ion emitter 1 via the porous heating element 2', and the melt reservoir 5 can be replenished with ionized metal as necessary. This makes it possible to achieve even longer life.

〔Effect of the invention〕

As described above, according to the present invention, the amount of ionized metal contained in the porous heating element, that is, the loading amount changes depending on the porosity of the porous heating element. Since the metal is not mounted in an exposed state, the amount of evaporation around the ion source can be reduced, and by using a melt reservoir for ionized metal, the service life can be extended.
EHD ion source can be provided.

[Brief explanation of drawings]

FIG. 1 is a front view showing the structure of a conventional field ionization liquid metal ion source, in which a shows a normal hairpin-shaped source and b shows a case in which the amount of ionized metal loaded is increased using an auxiliary line. FIG. 2 shows an example of the structure of the diffusion-supplemented field ionization liquid metal ion source of the present invention, a
is a hairpin-shaped front view, b is a coil-shaped front view,
c is a partially longitudinal front view of the case where a melt reservoir is attached to a. 1: Ion emitter, 2': Porous heating element, 5:
Melt reservoir, 6: Melt of ionized metal.

Claims (1)

[Claims] 1. A diffusion replenishment type EHD ion source characterized by comprising an ion emitter with a needle-like tip and a porous heating element containing ionized metal. 2 The ion emitter is made of W, Mo, Re, Ta, Ni or an alloy thereof, and the ionized metal is Ga,
The porous heating element is made of In, Au, Bi, Pb, Li, B, Cs, Al or an alloy thereof, and the porous heating element is made of W, Mo,
The diffusion replenishment type EHD ion source according to claim 1, characterized in that it is made of Re, Ta, Ni, or an alloy thereof.