JPS6276242A - Ion source - Google Patents

Abstract

PURPOSE:To stabilize taking out of ions even in case of highly reactive metal by employing polycrystal material produced through gas phase growth or single crystal boron nitride for a needle anode in a liquid metal ion source. CONSTITUTION:A liquid metal ion source comprises a reservoir 4 made of low reaction material such as carbon for holding an ionizing metal under fused condition, a heater 3, a needle anode 7 and an ion take-out electrode 10. Here, the needle anode 7 is formed with polycrystal material produced through gas phase growth or single crystal boron nitride (PBN). When ionizing such liquid metal as containing highly reactive metal such as aluminum or alloy, reaction with the needle anode 7 is retarded. Consequently, ions can be taken out efficiently and stably for long time resulting in long service life.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an ion source, and particularly to an ion source that uses highly reactive metals or alloys. The present invention relates to a shaped anode member.

(Prior art and its problems) Liquid metal ion sources can easily obtain high-brightness, minute-diameter ion beams, so they are useful for maskless ion implantation in electronic device manufacturing, ion beam etching, and microfabrication such as thin film formation. It is expected to be applied to technology. In the liquid metal ion source, a fine wire (about 0.2 mm in diameter) of a heat-resistant metal used to form an emitter metal wire is made into a needle shape with a tip radius of several μm by electropolishing, and the surface of the needle is coated with liquid metal. The liquid metal is wetted and ionized by a strong electric field applied to the tip.

The type of liquid metal loaded in the liquid metal ion source is selected depending on the intended use of the liquid metal ion source.

In particular, when the reactivity of the liquid metal is strong or when the melting point of the liquid metal is high, the reaction between the liquid metal and the emitter metal wire progresses easily. The disadvantage is that the material consumption is significant and the life of the liquid metal ion source is shortened.

An example of a highly reactive substance is aluminum (AQ).
A liquid metal consisting of Liquid metal ion sources made of aluminum are important for creating new electronic devices and for ion beam deposition, but typical liquid metal ion sources that use tungsten (W) as the emitter metal wire have a lifespan of only a few hours. It is only a matter of time, and is not of practical use. Further, since the emitter metal wire is eluted into the liquid metal, the elements constituting the emitter metal wire are also ionized, causing a decrease in the purity of emitted ions. In addition, boron (B) and silicon (
There is Si). These are platinum (pt)-boron (B),
It is used as a eutectic alloy of nickel (Ni)-boron (B), gold (Au)-silicon (Si), etc. to lower the melting point.

Although these liquid metal ion sources are expected to be used as ion sources for extracting boron ions for doping or silicon for self-ion sputtering, it is difficult to lower the melting point as described above. Moreover, a normal liquid metal ion source using tungsten as an emitter metal wire has an extremely short lifespan, and is not suitable for practical use.

In addition to tungsten, the emitter metal wires include tantalum (Ta), molybdenum (Mo), titanium (Ti), zirconium (Zr), and vanadium (■).

Alternatively, it is also possible to use a heat-resistant metal such as niobium (Nb), but even in this case, there is a drawback that the life is short, similar to when tungsten is used as the emitter metal wire.

In addition, JP-A-58-46542 discloses an ion source using either a conductive boride, a conductive composite boride, or a conductive carbide as a needle emitter. According to the specification, these borons and carbides are produced by forming needle-shaped high-melting point metal wires such as Ti, Zr, etc. into TiB,...
ZrB2. It is converted into TiC or the like. However, the life of the converted needle-shaped emitter is at most several to ten times longer than that of the metal wire emitter, and it has become clear that it is still not suitable for practical use.

(Object of the Invention) The object of the present invention is to eliminate the above-mentioned drawbacks and to achieve a longer life of a liquid metal ion source equipped with a highly reactive liquid metal, a high melting point metal, and a eutectic alloy. be.

(Structure of the Invention) In order to achieve the above object, the present invention includes a reservoir portion that melts and holds the metal to be ionized.

A needle-like anode having a needle-like tip to which molten metal is supplied from the reservoir, and a cathode (extraction electrode) for applying a high electric field to the tip of the anode in order to extract ions from the tip of the anode. In a liquid metal ion source having a liquid metal ion source, the above object is achieved by constructing the needle-shaped anode member with boron nitride.

(Example) The insulator is made of mink. Reference numerals 2 and 2' denote two stems for fixing the ion source, which are made of Kovar, for example, and are welded to the insulator 1 at appropriate intervals with silver solder, metallic glass, or the like. 3 and 3' are heaters made of fine wires of high melting point metals such as tungsten (W), tantalum (Ta), and molybdenum (Mo), and one end of each is made of carbon, P, etc.
It is fixed to a reservoir 4 made of a material with low reactivity such as BN or ceramic, and the other end is welded to the stem 2, 2' through the socket 1.

The reservoir 4 has a pore 5 in its lower part and a pore 6 in its upper part.
, PBN needle-shaped anode 7 with a polished tip radius of 1 to 10 μm
is penetrated.

The needle-shaped anode 7 protruding upward from the pore 6 at the upper part of the reservoir 4 is fixed at one end by an anode fixing member 8 made of a high melting point metal (for example, T a ), and the other end is fixed to the stem 2 . ing.

A heating power source (not shown) floating on the voltage of an accelerating power source (not shown) is connected to the stems 2, 2', and heats the heater 3, 3' to ionize the metal placed in the reservoir 4. 9 is melted. The cathode (ion extraction electrode) 10 is connected to an ion extraction power source (not shown). A voltage of 5 to 10 KV is applied between the acicular anode 7 and the ion extraction electrode 10, and a strong electric field is formed at the tip of the acicular anode 7 to the extent that ions can be field-emitted. Note that an ion accelerating voltage of several kilovolts to about 200 kilovolts is applied between these and the earth potential depending on the purpose.

In the above structure, current is passed through the stems 2, 2' to the heaters 3, 3' to heat the reservoir 4 and heat the metal or eutectic alloy 9 inside to a temperature above its melting point, turning it into a liquid.

In this state, ions are extracted and between the electrode 10 and the
When a voltage of KV is applied, the pulling force due to the electric field and the force returning in the opposite direction due to the surface tension of the liquid metal are balanced at a certain critical value of the electric field, and the tip of the needle-shaped anode 7 (lower end of the figure) Vertical angle 98. called TaylorCone.
It has a 6° conical shape. The electric field at this time was several 77 people (
angstrom), ionization occurs by field evaporation, and ions are extracted. The liquid metal lost due to ion extraction is pulled from the prepared hole 5 of the reservoir by electrostatic force, moves on the well-wet anode surface, and is supplied to the tip of the needle-like anode 7.

In this way, an ion beam can be obtained continuously.

By the way, conventionally, tungsten, titanium, their conversions, and the like have been used as the material for the needle-shaped anode 7, as described above, and tungsten, tantalum, etc. have been used for the reservoir 4 as well. However, highly reactive metals such as AQ
, B react with the above members at high temperature, and the reservoir 4
Impurities dissolve into the liquid metal 9 and cause a significant reaction with the needle-shaped anode 7, causing the tip of the needle-shaped anode 7 to become rounded and making it impossible to apply a high electric field to the needle tip. This caused a decisive inconvenience in that the emissions of the engine stopped completely. According to experiments, its lifespan is 1
Even the improved version takes only a few hours, which is extremely short. (However, in experiments, for example, in the case of B alone, the melting point is too high at 2300°C, so the melting point of B-Pt is 83°C.
0℃, B-Pd melting point 845℃, Pd-N1-B melting point 67
Binary and ternary eutectic alloys are used at fairly low temperatures, such as 5°C, but even then their lifespan is short. ) On the other hand, in the embodiment of the present invention, PBN was used as the material for the needle-shaped anode 7. As the PBN, for example, BORALLOY (trade name, Union Carpai 1~) was used. (Glass-like carbon was used as the material for the reservoir 4.) AQ, which has strong reactivity, was used as the liquid metal. As a result, the PBN acicular anode did not react with -AQCB (which was the same with many other highly reactive metals).

In addition, regarding wetting to stably supply ions to the anode tip, wetting with molten AQ (the same was true for many metals including B-based eutectic alloys) is very good. It was confirmed that this material is optimal as a needle material for ion sources.

In the above example, in which a life of more than 100 hours was confirmed through experiments, glassy carbon is used as the material for the beam reservoir 4, which is because this material is compatible with many metals including highly reactive metals such as AQ. This is because the wetness is poor. If the reservoir is too wet, there is a risk that the metal in the server will gradually come out through the slight gap in the reservoir 4.

Although this example has been explained using AQ (eutectic alloy of AQ and B, etc.), materials that can wet the PBN needle well and are less likely to wet the crucible material are not limited to the above materials. Of course, other eutectic alloys and single metals with weak or no reactivity can be widely used depending on the purpose, as long as they have good wettability with PBN.

Figure 2 is an example of the mass spectrum of the AQ ion source of the present invention measured using a single-focusing magnetic field mass spectrometer. No peaks of impurities due to elution of the anode material or server material were observed, and the result was extremely good. It can be seen that this is an AI2 ion source.

(Effects of the Invention) As explained above, the ion source of the present invention using PBN as the needle-shaped anode has the effect of operating stably for a long time as an ion source for liquid metals containing highly reactive metals and alloys.

[Brief explanation of drawings]

FIG. 1 is a front sectional view of an ion source according to an embodiment of the present invention. FIG. 2 is an example of a mass spectrum of the AQ ion source of the present invention. 1-111 insulator, 2.2'---- stem, 3.3'-
-Heater, 4-----reservoir, 5.6----hole. 7----Acicular anode, 8-111 Needle-shaped anode fixing member, 9
--Molten metal.

Claims (2)

[Claims] (1) A reservoir for melting and holding the metal to be ionized, a needle-shaped anode having a needle-like tip to which the molten metal is supplied from the reservoir, and a mechanism for extracting ions from the tip of the anode. 1. A liquid metal ion source comprising: a cathode (extracting electrode) for applying a high electric field to the tip of the anode; and the acicular anode member is made of boron nitride. (2) Claim 1, characterized in that the boron nitride is a boron nitride polycrystal or single crystal (pyrolytic boron nitride, abbreviated as PBN) produced by a vapor phase growth method. ion source.