JPS593815B2 - ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion source, and more particularly to an ion source using an alloy as the substance to be ionized.

Ion beam exposure using a metal ion source can expose fine patterns because the diffusion of ions within the photoresist is smaller than exposure using an electron beam.

Maskless ion implantation is also possible by narrowing down metal ions and irradiating them onto a desired fine region on a semiconductor wafer.

Therefore, microfabrication using ions is attracting attention as a future technology for manufacturing VLSIs, and research into metal ion sources suitable for this is actively conducted in various fields.

This kind of ion source usually places the substance to be ionized in a reservoir, heats the substance directly or indirectly by heating the reservoir, turns the substance into a liquid, and sharpens the liquid substance to a tip with a diameter of about 1 μm. is guided to the tip of the needle-shaped member, and ionized by a strong electric field formed near the tip.

Such an ion source requires heating the substance to make it into a liquid state, and therefore a substance with a high melting point cannot be used alone as an ionizing substance.

As a result, the melting point of an alloy is generally lower than the melting point of the substance that makes up the alloy, so in order to obtain ions of a substance with a high melting point, the alloy containing that substance is placed in the above-mentioned reservoir and heated to form a liquid. There is.

For example, if you want to obtain boron (B) ions with a melting point of 2000°C or higher, use Pt-B (alloy Pt-B) with platinum (Pt).
(melting point 79-5°C), the Pt-B is heated to a liquid state, pt ions and B ions are generated by a strong electric field, and an ion beam containing a mixture of both ions is heated using a Wien beam consisting of orthogonal electric and magnetic fields. The ions are then introduced into a separator such as a type of mass separator to obtain only B ions.

By the way, in the ion source using the above-mentioned alloy,
Tungsten is usually used as the needle-like member, and the surface portion of the member reacts with the liquid alloy and melts into the alloy.

Therefore, the resulting ion beam will contain extra member metal ions, and a new alloy will be created by melting tungsten into the liquid metal.

New alloys containing this tungsten, such as Pt-
B-W has a high melting point, and when heated to about the melting point of, for example, Pt-H, it solidifies and forms a lump.

This lump impairs the flow of liquid metal from the reservoir to the tip of the needle-like member, and as a result, the generation of the ion beam becomes unstable and becomes unusable.

The present invention has been made in view of the above points, and an object of the present invention is to provide an ion source using an alloy that can generate a stable ion beam over a long period of time.

The ion source according to the present invention liquefies the alloy by heating the alloy, guides the liquid alloy to the needle-like tip of the needle-like member, and ionizes it by a strong electric field formed near the needle-like tip. In such an ion source, at least a surface portion of the needle member is formed of a metal constituting the alloy.

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

FIG. 1 shows a cross-sectional view of an ion source which is an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line A-A' in FIG.

In the figure, reference numeral 1 denotes a reservoir containing an alloy such as Pt-B2, and the reservoir 1 is made of ceramic.

The reservoir 1 is supported by being sandwiched between two metal plates 3 and 4 that are easily deformable, such as tantalum, and the respective ends of the two metal plates 3 and 4 are aligned and spot welded. There is.

A pore 5 is provided at the bottom of the reservoir 1, and a needle-like member 6 made of platinum is placed through the pore 5.

One end of the needle-like member 6 is fixed to the metal plate by spot welding, for example, and the other end of the needle-like member is placed facing the extraction electrode 1. The diameter is sharpened to about 1 μm by a method such as etching.

The metal plates 3 and 4 are provided with a tungsten filament 8,
One end of the filament 8 is spot welded.
, 9 are welded to stems 11 and 12, respectively, which are fixed by insulators 10.

A ceramic coating 13 is applied to the surfaces of the metal plate 3.4 and the filaments 8 and 90.

Although not shown, since the stems 11 and 12 are connected to an extraction voltage power source and an acceleration power source, an extraction voltage of 5 KV to 10 KV is applied between the needle member 6 and the extraction electrode 1. An accelerating voltage of 20 KV to 100 KV is applied between the needle member 6 and the cathode 14 at ground potential, and a strong electric field is formed at the tip of the needle member 6.

In the configuration as described above, a heating current is supplied between the stems 11 and 12 from a heating power source (not shown), so that the tungsten filament 89 is heated.

As the filament is heated, the alloy 2 inside the reservoir 1 is heated by conductive heat, and when heated above the melting point of the alloy (Pt-B), the alloy becomes liquid.

The alloy that has become liquid inside the reservoir 1 passes through the pore 5 at the bottom of the reservoir 1 by a strong electric field at the tip of the needle-like member 6 and is drawn out to the tip of the needle-like member.

The liquid alloy at the tip becomes a Taylor cone (
It forms a conical protrusion called Ta1or Cone).

The diameter of the tip of this conical protrusion is extremely thin, about 0.03 μm, and therefore the electric field is extremely concentrated near the tip.

The alloy at the tip is evaporated and ionized by this strong electric field, and Pt ions and B ions are generated and accelerated by the cathode 14.

the accelerated ions are placed below the cathode 13;
For example, only B ions are selected by being guided to a Wien type mass separator (not shown) and used for ion implantation or the like.

In such an ion source, the diameter of the ion generating part is the needle-like member 6.
Since the diameter is approximately equal to the diameter of the tip of the conical protrusion made of alloy at the tip of the ion beam, the ion beam can be focused very narrowly, and a strong electric field is formed near the tip of the conical protrusion, making it possible to obtain a high-intensity ion beam. It is suitable for use in processing steps such as ion beam exposure and ion implantation in the VLSI manufacturing process.

Here, in the above-mentioned embodiment, since platinum is used as the needle member 6, even if the eutectic alloy Pt-B on which the platinum is based becomes liquid, the platinum on the surface of the member is It does not dissolve in the liquid alloy.

Therefore, the composition ratio of the liquid alloy does not change even after long-term use, and as long as the heating temperature is above a certain temperature, the alloy is stably supplied to the tip of the needle member 6 without solidifying.

In this example, a eutectic alloy of platinum and boron was used as the alloy, and platinum was used as the needle member, but other combinations, such as a eutectic alloy of gold and silicon (Au-
8i) and gold may be used as the needle-like member,
Other alloys such as Pd-Ni-B-As may also be used depending on the purpose of use.

Furthermore, in the above embodiment, since ceramic is used as the material for the reservoir 1, the reservoir material and the liquid alloy will not react and the material will not melt into the alloy, and the components and composition ratio of the alloy will be long. remains constant over time.

Furthermore, since the surfaces of the tungsten filaments 8 and 90 are coated with ceramic, the liquid alloy that has reached the filament portion through thermal diffusion reacts with the tungsten filament, causing the tungsten to melt into the alloy. As a result, the diameter of the filament becomes thinner, and there is no risk of that part being heated more and breaking.

Furthermore, since the metal plates 3 and 4 are also coated with ceramic, the metal plate material is prevented from melting into the liquid alloy.

As described in detail above, the ion source based on the present invention is capable of generating a stable ion beam over a long period of time.

The lake water invention is not limited to the embodiments described above and can be modified in many ways.

For example, although the entire needle-like member is made of a metal constituting an ionized alloy such as platinum, the central portion of the needle-like member may be made of another metal or a substance such as ceramic;
A metal constituting an ionized alloy, such as platinum, may be deposited on the surface of the material.

Alternatively, instead of using a container-like reservoir, for example, a needle-shaped member or a part of a filament may be wound into a coil, and the coil portion may be used as a reservoir to hold the alloy.

Furthermore, as a heating means, a heater is wound around the reservoir,
The reservoir and further the alloy to be ionized may be indirectly heated by radiant heat from the heater.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an ion source according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along line AA' in FIG. 1: Reservoir, 2: Alloy, 3, 4: Metal plate, 5: Pore,
6: needle-like member, γ: extraction electrode, 8°9: filament, 10: insulator, 11.12: stem, 13: ceramic coating, 14: cathode.

Claims (1)

[Claims] 1. An ion source in which the alloy is liquefied by heating the alloy, the liquid alloy is guided to the needle-like tip of a needle-like member, and ionized by a strong electric field formed near the needle-like tip, An ion source characterized in that at least a surface portion of the needle-shaped member is formed of a metal constituting the alloy.