JPH02234329A - Liquid metal ion source - Google Patents

Abstract

PURPOSE:To obtain an ion beam having practical lifetime and stability by constituting a needle-shaped electrode with tungsten boride in a liquid metal ion source emitting a platinum ion and a silicon ion from the tip of the needle- shaped electrode due to the effect of electric field. CONSTITUTION:The powder of tungsten boride is sintered and molded with a hot press molding machine according to the predetermined condition. The boride compact obtained is cut into rods having the predetermined size, using a wire cut electric discharge machine, and the tips of each rod is mechanically polished, thereby forming a needle-shaped electrode 1 having a conical tip. At both sides of the needle-shaped electrode 1, there are arranged reservoirs 2A and 2B, glassy carbon divisions 3A and 3B, thermal cracking carbon heaters 4A and 4B and stainless steel electrodes 5A and 5B. Consequently, the electrode 1 and the reservoirs 2A and 2B are free from abnormality after long operation. According to the aforesaid construction, the regulation of an ion beam becomes low, and there occurs no erosion of the needle shaped electrode 1 due to platinum-silicon alloy, thereby ensuring a stable ion beam for a long hour.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention heats and melts an alloy mainly composed of platinum and silicon, and applies a high electric field to generate a beam of high-intensity platinum ions and silicon ions. The present invention relates to a liquid metal ion source that emits liquid metal ions.

(Prior technology) Focused ion beam technology using a liquid metal ion source can obtain a very narrow ion beam with a diameter of about 0.1 μm, so it is useful for photomask modification, maskless ion implantation, and ion implantation. Applications in the semiconductor field such as beam exposure are expected.

In the field of maskless ion implantation, silicon (
St) is required. Since silicon alone has a high melting point and is difficult to melt, a gold-silicon-beryllium alloy (e.g. ＾us*sizJe., numerical value is atomic ratio, melting point approximately 400°C) is usually used, and the melting time is about 1000 hours. An ion source with a lifetime of
189545).

Recently, as semiconductor manufacturing technology advances, there is a desire to narrow down the diameter of a focused ion beam. Since the diameter and angular current density of a focused ion beam are generally limited by chromatic aberration, it is important to reduce the energy distribution of the ion beam in order to obtain a narrow ion beam. The energy distribution of the silicon ion beam is better than that of platinum-silicon (PtSi) than when using a gold-silicon-beryllium alloy.
It is smaller when using an alloy (Reference: H, ^rimo
to :J. Vac. Scl. Technol. B
6 (3), May/Jun 1988)
.

Therefore, platinum... A narrower silicon ion beam can be obtained by using a silicon alloy.

(Problems to be Solved by the Invention) However, platinum-silicon alloys have relatively high melting points, such as Pt. The melting point of tSiz: + (atomic ratio) is 850
℃, and in the case of conventionally used tungsten needle electrodes, the tungsten is eroded by the alloy and reaches the end of its life in a few hours. In addition to this, needle-shaped electrodes made of chromium boride are also known, but in this case as well, it has been found that they have a lifespan of more than 10 hours, and a platinum-silicon alloy liquid metal ion source with a practical lifespan has been obtained. I couldn't. An object of the present invention is to provide a platinum-silicon alloy liquid metal ion source that has a practical life and provides a stable ion beam.

(Means for Solving the Problems) The present invention supports an alloy mainly composed of platinum and silicon on the surface of a needle-like electrode, and by the action of an electric field, platinum ions and silicon ions are released from the tip of the needle-like electrode. The liquid metal ion source is characterized in that the needle-shaped electrode is made of tungsten boride.

In the present invention, tungsten boride and beam J-. W.B.
, l'l! A typical example is a compound such as BS, but it may also be a non-stoichiometric compound of W and B, or a mixed crystal of W and B. The needle-shaped tungsten boride electrode can be made of a sintered body of tungsten boride processed into a needle shape, a single crystal of tungsten boride processed into a needle shape, or a high-melting point metal such as tungsten, tantalum, or molybdenum. It may be processed into a needle shape and coated with tungsten boride on its surface.

A method for manufacturing these needle-like electrodes will be explained. First, in the case of a sintered body of tungsten boride, a small amount of metal powder such as iron, nickel, or cobalt is added as a binder to the tungsten boride powder, and a hot press molding machine is applied to the pressure of 100 kg/cflI or more. temperature 1600
Sinter mold at ~2100°C. Note that if too much binder is added, the problem of intergranular corrosion due to the platinum-silicon alloy will occur when the sintered body is used as a needle electrode, so it is desirable to keep the amount of binder used to the minimum necessary. A single crystal of tungsten boride is manufactured by a floating zone method or the like. To process a sintered body or single crystal of tungsten boride into a needle shape, first process it into a needle shape by electrical discharge machining, if necessary, and then sharpen the tip by mechanical polishing or electrolytic polishing to reduce the curvature of the tip. radius 1~2μm
Do the following. To manufacture a needle-shaped electrode coated with tungsten boride, the radius of curvature of the tip must be adjusted to 1 to 2 μm in advance.
Tungsten boride may be coated on the surface of a high-melting point metal polished to a thickness of m or less by a CVD method, a plasma spraying method, or the like.

It is sufficient to use the alloy whose main components are platinum and silicon in an amount that covers the surface of the needle-shaped electrode, but in order to use it for a long time, it is preferable to provide a reservoir for storing the alloy along with the needle-shaped electrode. The reservoir is a high melting point metal such as Ta, W, Mo, etc.
ic. ．． Carbide such as ZrC, TaC, WC, TiB2, ZrB. , TaB, WB, CrB2 and other borides, and TtN% TaN and other nitride molded bodies are used. Among these materials, tungsten boride is preferred because it has excellent corrosion resistance against platinum-silicon alloys as described above. The structure of the reservoir may be any structure as long as it can store the alloy in liquid form and supply it stably to the needle-like electrode, but it may include a base having an inner surface matching the outer shape of the base of the needle-like electrode and a recess for storing the alloy. Preferably.

Preferably, a heater is provided to keep the alloy in a liquid state. The heater preferably has a structure in which a block of carbon such as glassy carbon or pyrolytic carbon is pressed against a needle-shaped electrode to supply electricity to the carbon block. In particular, if the reservoir is made of a highly conductive material such as tungsten boride, and the needle electrode, reservoir, and heater are pressed together in this order, it is easy to supply electricity to the heater, and a liquid metal ion source with a stable structure can be obtained. . In this case,
If a partition wall made of a conductive material that has low leakage with the liquid alloy, such as a carbon plate, is provided between the reservoir and the heater, it is possible to prevent the liquid alloy from penetrating into the heater.

(Example) Hereinafter, the present invention will be specifically explained using Examples 1 to 3 and Comparative Examples 1 to 3. Powders of each of the borides shown in the table are used as materials for needle electrodes by hot pressing at a temperature of 2000°C.
Pressure sintering was performed for 30 minutes at a pressure of 150 ksr/cd to produce a boride molded body. The relative density of all boride molded bodies was 95% or more. The boride molded body was processed using a wire cassette discharge machine.Q, 5 Tsuru 5
It was cut into sticks of 5 cranes each. Machine polish the tip,
A needle electrode with a conical tip was used. The cone angle of the cone is 30
degree, and the radius of curvature of the tip of the cone was 2 μm.

Next, a molded body of the same boride as the needle-shaped electrode was processed by wire-cut electrical discharge machining to produce a spoon-shaped reservoir with a curved tip. As shown in FIG. 1, on both sides of the needle electrode 1, there are reservoirs 2A, 2B, partition walls 3A, 3B made of glassy carbon, and a heater 4 made of pyrolytic carbon.
A, 4B and stainless steel electrodes 5A, 5B are arranged, bolts 6, insulating washers 7A, 7B and nut}8A, 8
These parts were fixed by tightening with B.

Note that the electrodes 5A and 5B are connected to the terminal 1 through the metal plates 9A and 9B.
It is connected to 0A and IOH, and the terminal is fixed to the insulator 1l.

The liquid metal ion source obtained in this way was installed in a vacuum device and a vacuum was created at a pressure of 2 × 10 −” Torr.In this vacuum device, a platinum-silicon alloy (
A crucible made of boron nitride filled with PbtSit3-atomic ratio) was placed therein, and the crucible was heated to melt the alloy. While heating the needle electrode by applying electricity to the heater of the liquid metal ion source, the tip of the needle electrode is dipped into the molten alloy in the crucible, causing the molten alloy to rise along the needle electrode, and the needle electrode and the reservoir are heated. Alloy was stored in between.

The liquid metal ion source produced in this manner was attached to another vacuum device, and the inside of the device was evacuated to a pressure of 8×10 −′ Torr. Power is applied to the heater of the liquid metal ion source, and the temperature at the tip of the needle electrode is adjusted to 10% by brightness temperature by adjusting the current.
The temperature was set to 00℃. Note that the brightness temperature was measured using an optical pyrometer.

1. From the tip of the needle electrode. An extraction electrode made of a perforated metal disk was provided at a distance of 50 mm, and an ion beam with a current of 10 μA was emitted by adjusting the voltage applied to the extraction electrode. The ion beam was continued to be emitted in constant current mode, the fluctuation of the extraction voltage was measured, and the ion beam fluctuation rate was determined using the following formula.

Upon observation, it was found that the needle electrode had been eroded by the platinum-silicon alloy, and the radius of curvature at the tip of the needle electrode had increased to 10 μm or more.

Table Esax: Maximum value of withdrawal voltage for 10 minutes [! -1-
: As is clear from the table of minimum extraction voltages for 10 minutes, the ion beam variation rate is 0. It was good at 3% or less. After operating for 150 hours, the liquid metal ion source was taken out from the vacuum apparatus and observed, but no abnormality was found in the needle electrode or reservoir.

On the other hand, in the case of a liquid metal ion source that uses chromium boride, titanium boride, or zirconium boride for the needle electrode and reservoir, the ion beam fluctuation rate is large, as shown in the table, and the ionization takes 5.5 to 11 hours. Beams can no longer be emitted. Taking out the liquid metal ion source from the vacuum apparatus (effects of the invention) The liquid metal ion source of the present invention has a small ion beam fluctuation rate, and there is no erosion of the needle electrode by the platinum-silicon alloy.
It can be used stably for a long time.

[Brief explanation of the drawing]

FIG. 1 is a front view of the liquid metal ion source of the present invention. sign 1. Single needle electrode, 3A/3B-bulkhead, 5A/5B/one electrode, 7A/7B - Insulating washer, 9A/9B - metal plate, 11 insulators. 2A/2B-Reservoir, 4A/4B- Heater 6.-volt, 8A/8B-nut, 10A-10B one terminal,

Claims (1)

[Claims] A liquid metal ion source in which an alloy containing platinum and silicon as main components is supported in a liquid on the surface of a needle-shaped electrode, and platinum ions and silicon ions are emitted from the tip of the needle-shaped electrode by the action of an electric field. A liquid metal ion source characterized in that the source consists of tungsten boride.