JP2517678B2 - Liquid metal ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention heats and melts an alloy containing palladium and arsenic as main components, and applies a high electric field to generate a beam of at least arsenic ions with high brightness. It relates to a source of liquid metal ions to be emitted.

(Prior Art) Focused ion beam technology using a liquid metal ion source is
Since it is possible to obtain an extremely thin ion beam having a diameter of about 0.1 μm, it is being applied to semiconductor fields such as photomask correction, maskless ion implantation, and ion beam exposure.

Regarding maskless ion implantation of a silicon semiconductor, ionic species of boron as a P-type dopant and phosphorus or arsenic as an n-type dopant are required. In particular, arsenic sublimes at 615 ° C. under 1 atm and has an extremely high vapor pressure, so it is difficult to use arsenic simple substance as an ionized substance of a liquid metal ion source.

Therefore, other metals and arsenic were alloyed to reduce the vapor pressure of arsenic. One example was Sn-Pb-A.
Alloys such as s, Pd-As, and Pd-As-Cu have been proposed. However, in any of the alloys, the vapor pressure could not be lowered sufficiently and it reacted with the needle electrode, so that the life of the ion source was only ten and several hours.

Therefore, recently, a liquid metal ion source using Pd ₂ As alloy and tungsten for the needle electrode was developed, and its life is
It has been reported that it was 150 hours [Journal. of. Vacuum. Science. Technology (Journal of Vacuum Science Technology) Volume B5, No.
1, pp. 197-202 (1987)]. However, although this liquid metal ion source has been improved, it was not possible to stably generate the target arsenic ion for a long time due to the reaction between the alloy and tungsten as the needle electrode. In particular, when the liquid metal ion source is immersed in the Pd ₂ As alloy and the immersion temperature is increased when the alloy is stored, the reaction is remarkable and there is a problem that it is difficult to industrially utilize.

(Problems to be Solved by the Invention) In the prior art, it was not possible to obtain a liquid metal ion source that emits a stable arsenic ion beam for a long time due to a small reaction between the alloy and the needle electrode.

An object of the present invention is to provide a liquid metal ion source of palladium-arsenic alloy which can obtain a stable ion beam with good reproducibility and has a practical life.

In order to achieve this object, the present inventors diligently studied the material of the needle-shaped electrode that is extremely difficult to react with the palladium-arsenic alloy, as a result, tungsten boride, molybdenum boride, chromium boride, their compounds, and The inventors have found that a mixed crystal or mixture of tungsten boride, molybdenum boride and chromium boride is most suitable, and completed the present invention.

(Means for Solving the Problem) That is, the present invention is summarized as follows.

A liquid metal ion source that supports an alloy containing palladium and arsenic as a main component on the surface of a needle electrode with a liquid, and emits at least arsenic ions from the tip of the needle electrode by the action of an electric field, wherein the needle electrode is A liquid metal ion source characterized by comprising a VI A group boride.

 Hereinafter, the present invention will be described in more detail.

In the present invention, the boride of Group VI A element means tungsten boride (WB, W ₂ B, W ₂ B _5, etc.), molybdenum boride (M
oB ₂ , Mo ₃ B ₂ , MoB, etc., Chromium boride (Cr ₃ B ₂ , CrB, C
r ₄ B), their compounds, and a mixed crystal or mixture of tungsten boride, molybdenum boride, and chromium boride.

Further, the needle-like electrode means an electrode having a needle-like tip at least.

The needle electrode 1 in FIG. 1 is a single crystal or sintered body of VIA group element boride processed into a needle shape, or a high melting point metal such as tungsten, tantalum, or molybdenum processed into a needle shape, The surface thereof may be coated with a boride of Group VI A element described above.

Next, a method for manufacturing these needle-shaped electrodes will be described. For example, in the case of tungsten boride, a small amount of metal powder such as iron, nickel, or cobalt as a binder is added to the powder of tungsten boride, if necessary, pressure 100 kg / cm ² or more by a hot press molding machine, temperature 1600 ~ Sinter molding at 2100 ℃. If too much binder is added, the problem of intergranular corrosion due to palladium and arsenic alloy occurs when the sintered body is used as a needle-shaped electrode, so it is desirable to keep the amount of binder used to the minimum necessary. .

To process a needle-shaped electrode from a tungsten boride single crystal or sintered body, if necessary, first process it into a needle shape by electrical discharge machining, then sharpen the tip by mechanical polishing or electrolytic polishing to make the curvature of the tip. The radius is set to 1 to 2 μm or less.

To manufacture a needle electrode coated with tungsten boride, tungsten boride is CVD-coated on the surface of a refractory metal whose tip has a radius of curvature of 1 to 2 μm or less.
Method, plasma spraying method, or the like. In the case of molybdenum boride, chromium boride, tungsten boride, their compounds and their mixed crystals or mixtures, they can be produced by the same method.

As the alloy containing palladium and arsenic as the main components, for example, in the case of the Pd-As element, one having a Pd / As (atomic ratio) of 5 to 1 is used, and it is produced by the following method. Palladium and arsenic powders are mixed evenly in an atomic ratio of 2: 1, put in a quartz ampoule, and then sufficiently replaced with argon, which is an inert gas, and then 850 ° C in an electric furnace in a reducing atmosphere.
It is manufactured by heating and melting at the above temperature. The resulting alloy had an atomic ratio of palladium to arsenic of 75:25.

An alloy containing palladium and arsenic as the main component is sufficient to cover the surface of the needle-shaped electrode, but for long-term use, the reservoir (the 2A and 2B in FIG. 1) for storing the alloy is needle-shaped. It is preferable that the electrodes are provided side by side. The reservoir is Ta,
Refractory metals such as W and Mo, carbides such as TiC, ZrC, TaC and WC, borides such as TiB ₂ , ZrB ₂ , TaB ₂ , CrB ₂ and W ₂ B ₅ ,
Nitride formers such as TiN and TaN are used. Among these materials, tungsten boride and chromium boride are preferable because they have excellent corrosion resistance to the above-described palladium-arsenic alloy.

The structure of the reservoir may be such that the alloy can be stored in a liquid and can be stably supplied to the needle electrode.
It is preferable that the needle-shaped electrode is provided with a base having an inner surface conforming to the outer shape of the base and a recess for storing the alloy.

A heater (Fig. 1A, 4A,
4B) is preferable. The heater may have a structure in which a carbon block such as glassy carbon or pyrolytic carbon is pressed against the needle electrode to energize the carbon block. In particular, if the reservoir is made of a highly conductive material such as tungsten boride or molybdenum boride or chromium boride, and the needle electrode, the reservoir, and the heater are pressed in this order, it is easy and stable to energize the heater. It becomes the source of liquid metal ions in the structure. In this case, if a partition wall made of a conductive material having a poor leak property with respect to a liquid metal such as a carbon plate is provided between the reservoir and the heater, the liquid metal can be prevented from penetrating into the heater.

As a method of storing the alloy in the reservoir, a method such as brush coating has been conventionally performed, but recently, as a practical method of sufficiently filling the alloy, the melting point of the alloy in the crucible such as boron nitride is 150 to 150 A method of immersing the needle electrode and the reservoir in an alloy melted at a temperature higher than 300 ° C. has been adopted.

<Examples> Hereinafter, the present invention will be specifically described with reference to Examples.

(Examples 1 to 5, Comparative Examples 6 to 10) As the material of the needle-shaped electrode, the boride shown in Examples 1 to 5 of the table was used. This needle electrode was manufactured as follows. Powder of each material shown in the table at a temperature of 2000 ° C and a pressure of 200k
A compact was manufactured by pressure sintering with a hot press for 30 minutes in a vacuum of g / cm ² . The relative density of all molded products is 95
% Or more. These molded bodies were cut into rods of 0.5 × 0.5 × 5 mm by a wire cut electric discharge machine. The tip was mechanically polished to form a conical needle electrode. The cone angle of this cone was 30 degrees, and the radius of curvature of the tip of the cone was 2 μm.

Next, a molded body made of the same material as the needle-shaped electrode was processed by a wire cut electric discharge machining method to manufacture a spoon-shaped reservoir having a curved tip.

FIG. 1 shows the structure of the liquid metal ion source. Reservoirs 2A and 2B, anodes 3A and 3B made of glassy carbon, and a heater 4 made of pyrolytic carbon are provided on both sides of the needle electrode 1.
A, 4B and electrodes 5A, 5B made of stainless steel were arranged and tightened with bolts 6, insulating washers 7A, 7B and nuts 8A, 8B to fix these parts. The electrodes 5A and 5B were connected to the terminals 10A and 10B via the metal plates 9A and 9B, and the terminals were fixed to the terminals.

The liquid metal ion source is installed in a vacuum device and the degree of vacuum is 2.0.
It was set to × 10 ^-6 torr. A crucible made of boron nitride, which was previously filled with a palladium arsenic alloy (Pd ₇₅ As ₂₅ melting point 750 ° C), was placed in this vacuum device, and the crucible was heated to 90 ° C.
The alloy was kept melted at 0 ° C. While energizing the heater of the liquid metal ion source to heat the needle electrode, the needle electrode and the reservoir were immersed in the molten alloy in the crucible to collect the alloy between the needle electrode and the reservoir.

For comparison, it was carried out by changing the material of the needle-shaped electrode and the method of storing the alloy between the needle-shaped electrode and the reservoir. For the materials (W, TiB ₂ , ZrB ₂ , WC) shown in Comparative Examples 6 to 10 in the table, a liquid metal ion source was manufactured by the same method as above, and an alloy was formed between the needle electrode and the reservoir by the same method. I collected it.

The liquid metal ion source thus produced was attached to another vacuum device. Comparative Example 10 adopted a method in which the method of collecting the alloy between the needle electrode and the reservoir was changed. That is, powder of Pd ₇₅ As ₂₅ (particle size 10 to 50 μm) is mixed with methanol in the reservoir so as to have a squeeze, and a small brush is applied into the reservoir. Then, the ion source was quickly installed in a vacuum device so as not to give vibration, and a vacuum was drawn up to 2 × 10 ⁻⁶ torr. The heater of the ion source is energized to heat the needle-shaped electrode and the reservoir so that the melting point of the alloy is 50
It was kept at 800 ℃, which was higher by ℃, and melted. Then, the temperature was maintained and the alloy was wet and spread to the tip of the needle electrode.

The inside of the vacuum apparatus to which the liquid metal ion source was adjusted and attached was set to a vacuum degree of 8 × 10 ⁻⁷ torr. The heater of the liquid metal ion source was energized, and the temperature of the tip of the needle electrode was adjusted to a brightness temperature of 800 to 820 ° C by adjusting the current. The brightness temperature was measured with an optical pyrometer. An extraction electrode made of a perforated metal disk was provided at a distance of 1.5 mm from the tip of the needle electrode, and an ion beam with a current of 10 μA was emitted by adjusting the voltage applied to the extraction electrode. The ion beam emission was continued in the constant current mode, the fluctuation of the extraction voltage was measured, and the ion beam fluctuation rate was obtained by the following formula.

E _max : Maximum value of extraction voltage for 10 minutes E _min : 〃 Minimum value The results are shown in the table. WB, W ₂ B ₅ , MoB ₂ , CrB ₂ , WB + MoB ₂ + CrB ₂ (40, 30, _{3 for} the needle electrode and reservoir
In the case of the liquid metal ion source using 0% by weight), the fluctuation rate of the ion beam was as good as 1% or less. As a result of observing the ion source which has reached the end of life by removing it from the vacuum chamber, W
_In the ion source using ₂ B ₅ , MoB ₂ , and CrB ₂ , the needle electrode and the reservoir did not appear to react with the alloy. In the case of WB, the radius of curvature of the tip was 3 μm, which was larger than that before impregnation, and a slight reaction was observed. However, it did not pose a problem in practice.

On the other hand, W, TiB ₂ , ZrB ₂ and WC are used for the needle electrode and reservoir.
In the case of the liquid metal ion source using, the ion beam could not be emitted because the needle electrode and the alloy reacted when the reservoir was impregnated with the alloy or did not wet as shown in the table.

In the impregnation method of Comparative Example 10, the alloy was not fully filled in the reservoir in one application, and the life was short, 50 hours.
Also, the stability of the beam was poor because the wetting of the needle electrode and the alloy was insufficient.

(Effects of the Invention) The liquid metal ion source of the present invention does not erode the needle-shaped electrode by the palladium-arsenic alloy, has good wettability, has a small beam fluctuation rate, and can stably emit an arsenic ion beam for a long time. It can be emitted and can be used stably.

[Brief description of drawings]

 FIG. 1 is a front view of a liquid metal ion source of the present invention. 1 ... Needle electrode, 2A, 2B ... Reservoir, 3A, 3B ... Septa, 4A, 4B ... Heater, 5A, 5B ... Electrode, 6 ... Bolt, 7A, 7B ... Insulation washer, 8A, 8B: Nut, 9A, 9B ... Metal plate, 10A, 10B ... Terminal, 11 ... Insulator.

Claims (1)

(57) [Claims] 1. A liquid metal ion source in which an alloy containing palladium and arsenic as main components is supported on a surface of a needle electrode by a liquid, and arsenic ions are emitted from the tip of the needle electrode by the action of an electric field. A liquid metal ion source, wherein the needle-shaped electrode is made of a boride of Group VI A element.