JPS6383264A - Liquid metallic ion source - Google Patents

Abstract

PURPOSE:To prolong the service life of a liquid metallic ion source by manufacturing a needle anode in the liquid metallic ion source used for ion beam etching or the like with a high-m.p. metallic W wire and coating the surface thereof with the film of a B compd. CONSTITUTION:Two pieces of stems 2, 2' made of 'Kovar(R)' fixing an ion source are welded to an insulator 1 made of ceramic with silver solder or the like, the ends of heaters 3, 3' made of a high-m.p. metallic wire such as W, Mo and Ta are spot- welded to these stems 2, 2', and the other ends of the heaters are spot-welded by gas to heaters 4, 4' combined with a supporting late for a reservoir made of same high-m.p. metallic material as the above-mentioned metallic wire. A small hole 6 is pored to the bottom of the reservoir 5, a small hole 7 is pored to the upper part thereof, and a needle anode 8 made of a W wire which is mechanically abraded so as to obtain 1-10mum radius of the tip and 30-60 degree vertical angle and subjected to BN coating is penetrated through these small holes. A liquid metallic ion source which has prolonged service life and forms stable metallic ion ion beams is obtained by impressing 5-10kV voltage between this acicular anode 8 and an ion drawing electrode 11, forming an intensive electric field to the tip of the needle anode 8, and melting liquid metal 10 incorporated in the reservoir 5.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a liquid metal ion source, and in particular improves the wettability between its acicular anode member and highly reactive molten metal,
This invention relates to an ion source that can generate a stable ion beam for a long time.

(Prior Art) Liquid metal ion sources are expected to be used in various microfabrication techniques, such as maskless ion implantation, ion beam etching, and production of thin films with minute areas.

A liquid metal ion source is produced by forming the tip of a high-melting point metal into a needle shape with a radius of several μm using an electrolytic polishing method, wetting the surface with liquid metal to form an emitter, and applying a high electric field to the needle tip. It ionizes metal and extracts it as an ion beam.

FIG. 2 shows a schematic cross-sectional view of a conventional liquid metal ion source.

Fixing the ion source to the ceramic insulator 1 2
A heater 3 made of fine wire of high-melting point metal such as W, Ta, Mo, etc., whose stems 2, 2' made of Kovar are welded with silver solder, metallic glass, etc., and one end of which is spot welded to the stems 2, 2'. A reservoir support plate/heater 4, 4' made of the same high-melting point metal material as the heater is spot welded to the other end of the heater 3'.

The reservoir support plate/heater 4, 4' is made by winding the reservoir and welding it together. The reservoir 5 has a pore 6 at the bottom and a pore 7 at the top.
The radius of the tip is 1 to 107. A needle-shaped anode 8 polished to have an apex angle of 30 to 60 degrees passes through it. The upper part of the needle anode 8 that protrudes upward from the pore 7 is fixed to the stem 2 by arrow welding using a fixing member 9 made of a high melting point metal material.

Although not shown, a heating power source that floats on the voltage of an accelerating power source is connected to the stems 2 and 2'.
3', a reservoir support plate/heater 4°4' is heated to melt the metal 10 in the reservoir 5. Further, the ion extraction electrode 11 is connected to an ion extraction power source, and a voltage of 5 to 10 kV is applied between the needle anode 8 and the ion extraction electrode 11.
The voltage is marked.

A strong electric field is formed at the tip of the needle-like anode 8 in which ions can be emitted. Note that an ion accelerating voltage of several kV to 200 kV is applied between these and the earth potential, depending on the purpose of use.

The type of liquid metal loaded in a liquid metal ion source is selected depending on the purpose of use of the liquid metal ion source, but B (boron), which plays an important role in the creation of new electronic devices, and ion beam deposition Liquid metals such as AI (aluminum), which are important for applications, are highly reactive and easily react with the emitter metal wire, so the tip of the needle anode is worn out and the lifespan of the liquid metal ion source is shortened. There is.

Previously, the inventor of this application, in Japanese Patent Application No. 60-217366,
We proposed boron nitride as an emitter metal wire that does not react with these molten metals and has good wettability. However, since this material requires machining to obtain a needle-like shape, the diameter of the needle-like anode becomes large and requires at least 0.8 mm. The large diameter limits the amount of molten metal that can be accommodated in the reservoir section, thereby shortening the life of the liquid metal ion source. Increasing the amount of molten metal loaded by enlarging the reservoir portion increases the size of the ion source and is not practical.

Furthermore, when boron nitride is used, spot welding is not possible when fixing it to a needle-like anode stem, and a complicated structure such as screwing is required.

(Objective of the Invention) An object of the present invention is to solve the above-mentioned problems and to extend the life of a liquid metal ion source loaded with a highly reactive liquid metal or eutectic alloy.

(Means for Solving the Problems) The present invention comprises: a reservoir portion that melts and holds a metal to be ionized; a needle-like anode having a needle-like tip portion to which molten metal is supplied from the reservoir portion; The above object is achieved by a liquid metal ion source comprising: means for forming a strong electric field at the tip; and a liquid metal ion source in which a film of compound B is formed on the needle-shaped anode member .

(Example) Hereinafter, the present invention will be explained in detail using FIGS. 1a and 1b as an example.

W (tungsten) is used as the needle-shaped anode material. First, a W wire rod 80 with a diameter of 0.2 mm was soaked in nitric acid.

Wash with acetone, alcohol, etc., and use KOH aqueous solution to prepare a tip radius of 1 μm to 1071 m and a tip angle of 30° to 60°.
Process into a needle shape. Next, a commercially available liquid coating material B (trade name "Boron Coating"; manufactured by Denki Kagaku Kogyo ■) is applied to the lower part 81 of the wire 80 by spraying, dipping, or brushing, and Baking is carried out for about 15 minutes at a temperature of °C and then washed. The thickness of the resulting BN coating is approximately 0.05 mm.

FIG. 1a is an enlarged view of the BN-coated needle-shaped anode 8, and FIG. 1 is a schematic cross-sectional view of a liquid metal ion source constructed using the same.

The configuration is almost the same as the conventional device, and the two Kovar stems 2, 2' that fix the ion source are welded to a ceramic insulator using silver solder, metallic glass, etc., and the stems 2, 2' W, Ta, M with one end spot welded to
Reservoir support plates/heaters 4, 4' made of a high melting point metal material similar to the heaters are spot welded to the other ends of the heaters 3, 3' made of high melting point metal thin wires such as O. , 4' are wound around the reservoir and welded together. The reservoir 5 has a pore 6 at the bottom and a pore 7 at the top.
The radius of the tip is 1-10 μm, and the apex angle is 30-. A needle-like anode 8 mechanically polished at 60 degrees and coated with BN passes through it.

The upper part of the needle-shaped anode 8 that protrudes upward from the pore 7 is
Since it is not coated with BN, it is fixed to the stem 2 by spot welding to a fixing member 9 made of a high melting point metal material.

Although not shown, a heating power source that floats on the voltage of the accelerating power source is connected to the stems 2 and 2'.
3', a reservoir support plate/heater 4°4' is heated to melt the metal 10 in the reservoir 5. The ion extraction electrode 11 is connected to an ion extraction power source, and a voltage of 5 to 10 kV is applied between the needle anode 8 and the ion extraction electrode 110.
A voltage is applied, and a strong electric field is formed at the tip of the needle-like anode 8 in which ions can be field-emitted. Note that the distance between these and the earth potential is from several kV to 200 kV depending on the purpose of use.
An ion acceleration voltage of kV is applied.

With the above configuration, AI with the highest reactivity as the molten metal 9
was used, and the reservoir 5 was made of ceramics that were corrosion resistant to AI.

To explain the operation of this liquid metal ion source, the stem 2,
Electric current is passed through heaters 3 and 3' through heaters 3 and 3' to heat reservoir 5 and heat molten metal 9 above its melting point to liquefy it. In this state, apply 5 to 10 k to the ion extraction electrode 11.
When a voltage of V is applied, the pulling force due to the electric field and
The surface tension of the liquid metal balances the pullback force at a certain critical value, creating a cone with an apex angle of 98.6°, called a Taylor cone, at the tip of the needle-shaped anode 8. At this time, the electric field at the tip reaches several V/in, ionization occurs due to field evaporation, and ions are extracted.

The liquid metal lost due to ion extraction is drawn out from the pilot hole 6 of the reservoir by electrostatic force, moves on the well-wet anode surface, and is supplied to the tip of the needle-shaped anode 8. In this way, a continuous ion beam can be obtained.

Figure 3 is an example of the mass spectrum of the AI liquid metal ion source of the present invention measured using a single focusing magnetic field type mass spectrometer, but no impurity peaks due to elution of the anode material or reservoir material were observed. , AI has not reacted with the anode material beyond the BN coating. Furthermore, the BN coating was effective in stably supplying ions to the tip of the needle-like anode, resulting in very good wetting, and it was confirmed that it is optimal as an emitter material for liquid metal ion sources.

Experiments have confirmed that it has a lifespan of over 100 hours with a current of 30 μA (constant).

Furthermore, compared to the boron nitride emitter of the patented invention mentioned above, it has been confirmed that it is a liquid metal ion source that has a simple structure, can be manufactured easily, can be loaded with a large amount of AI, and has a long life. It was done.

Although AI is used in this example, the liquid metal material that can be used is not limited to AI, but any material that can wet the BN-coated needle anode well and does not easily react with it can be used. All can be applied. For example, a highly reactive eutectic alloy of B can be effectively used.

Furthermore, the coating material is not limited to BN either. This is because needle-like anodes coated with other compounds of B exhibit the same effects as described above.

(Effects of the Invention) The liquid metal ion source using the BN-coated acicular anode of the present invention can be used as an ion source for liquid metals containing highly reactive metals and alloys. It has the effect of generating a stable ion beam.

[Brief explanation of the drawing]

FIG. 1a is a schematic cross-sectional view of a liquid metal ion source of the present invention. Figure 1 is an enlarged view of the needle-shaped anode. FIG. 2 is a schematic cross-sectional view of a conventional liquid metal ion source. FIG. 3 is an example of a mass spectrum of the AI liquid metal ion source of the present invention. 1... Insulator, 2, 2'... Stem, 3.3'... Heater, 4.4'... Reservoir support plate and heater, 5.
・・・;・Reservoir, 6, 7... Details, 8・
...acicular anode, 10...molten metal, 11
······cathode,

Claims (2)

[Claims] (1) A reservoir section for melting and holding the metal to be ionized; A needle-like anode having a needle-like tip to which the molten metal is supplied from the reservoir section; A needle-like anode for forming a strong electric field at the needle-like tip; A liquid metal ion source comprising means and; characterized in that a film of a B (boron) compound is formed on the acicular anode member. (2) The liquid metal ion source according to claim 1, wherein the compound B is BN.