JPS5968142A - Emitter chip for field ionization gas ion source - Google Patents

Abstract

PURPOSE:To obtain an ion source with high field intensity and high radiation ion current density whose emission site is restricted to a specified area by making the work function of a member which forms a tip larger than that of a member which forms the bottom. CONSTITUTION:A zirconium (Zr) coat 21 is formed by covering the entire of an emitter chip 3 with a metal with the smaller work function than tungsten W that is the material of the emitter chip 3, for example zirconium Zr. In this case, since a tip 11' has exceedingly small curvature as compared with that of the bottom 11, field intensity is increased and the zirconium of this area evaporates due to electric field. At the bottom, the coat 21 is formed as it is. As a result, the work function of the emitter chip is set to the value possessed by tungsten W, i.e. approximately 4.6eV at the tip 11' and on the other hand it is set to the value possesed by zorconium Zr, i.e. approximately 4.1eV at the bottom 11. The ionization of gas particles are collectively generated near the tip 11'.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an emitter chip for a field ionized gas ion source. In particular, the present invention relates to an improvement in an emitter chip for a field ionization gas ion source in which ionization occurs only in a specific region and has a large radiation angular ion current density.

(2) Background of the technology Field ionization gas ion sources, field emission liquid metal ion sources, etc. are generally used as ion sources in methods using ion beams, such as ion beam etching and ion beam exposure. has been done.

A field ionization gas ion source is one in which ionized scum, such as hydrogen (j-12), helium (1-1e), argon (Ar), etc., is at a pressure of about 10-10 i'orr).

A high electric field of about 1 to 3 [■/A] is generated in the vicinity of the tip of a needle-like electrode, that is, an emitter tip, which is provided in a vacuum container supplied with the gas, and the gas is ionized by the electric field in this vicinity. This device releases these ions from the above-mentioned opening by means of an electrostatic field generated between a counter electrode having an opening, and has a basic structure as shown in FIG. In the figure,
1 is a vacuum container made of an insulator, 1' is a gas inlet, and 2 is a counter electrode, which has an ion ejection opening 2' with a diameter of about 1 mm. 3 is an emitter chip.

For such an ion source, it is desirable that the brightness is high, that is, the radiation angle ion current density is high. In order to increase the radiation angle ion current density, the curvature of the emitter tip should be made thicker to increase the number of gas molecules supplied to the tip of the emitter tip (and the ionization of gas molecules at the tip of the emitter tip should be increased). By the way, in a field ionization gas ion source, the ionization probability D when gas molecules are at the position jyBt where they are most likely to be ionized near the tip of the emitter tip is
It is given by the following equation.

However, in equation (1), ■) is the ionization probability of gas molecules, ■ is the ionization energy of gas molecules, φ is the work function of the emitter tip, and F is the electric field strength near the tip of the emitter tip. be.

As is clear from the above equation, in order to increase the ionization probability, (a) the ionization energy ■ of the gas to be ionized is small, (b) the Emi-Sotachi-Tsubu work function φ is large, and , (c) It is effective that the electric field strength F is large. On the other hand, in order to increase the current density of the radiation angle A and increase the brightness, one thing is to increase the curvature of the emitter tip so that the force of the gas molecules supplied to the tip of the emitter tip increases, and the emission site Emi
It is desirable to limit the treatment to a specific area at the tip of the tip.

(:3) Prior art and problems In the prior art, as a method of forming the above-mentioned emi-sosion site, (a) the tip of a needle-like member made of tungsten (W) or the like is made into a (100) plane; cottt-t
, a method of protruding the tip by so-called surface diffusion, heating at 500 K[lC and simultaneously applying an electric field of about 1 (V/A); Window element (N2), oxygen (U2),
A method has been used in which contamination is carried out using Charcoal'X (C) or the like, and only the contaminated area is used as an emission site. In the structure obtained by method (a), the selection of shapes is limited and stability and reproducibility are low. On the other hand, the structure obtained by method (b) has the disadvantage that the shape of the tip is determined completely heteronomously, resulting in poor controllability and reproducibility. Therefore, it is important to improve the emission site's structure: ;1j
is getting stronger.

(4) Purpose of the Invention The purpose of the present invention is to meet this demand, and the emitter chip has a large overall curvature, and a large number of gas molecules are supplied to the tip (and furthermore, the end of the 'ii++ specification). 1
The emission site where the f-function is large compared to the surrounding area is limited to a specific region, and the curvature at the emission site is small, so the electric field strength is thick (this describes an ion source with a large radiation angular ion current density). An object of the present invention is to provide an emitter chip for a field ionized gas ion source.

(5) Structure of the Invention According to the present invention, (a) there is provided an emitter chip for a field ionization gas ion source in which the work function of the member forming the tip portion is larger than the work function of the member forming the base portion; and in the configuration of (a) above, the tip) 51;
The material that makes up is tungsten (W) or iridium (I
r), and the member forming the bottom portion is made of zirconium (Z
An emitter dip for a field ionized gas ion source is provided, which is barium (L3a) or barium (L3a).

In the above equation, when the work function φ of the emitter tip is large, the ionization probability J) becomes large, but conversely, when the work function φ is small, the ion 1-hi probability J) becomes small. In other words, if the work function φ of the region other than the region that should be the emission site at the tip of the emitter tip is made smaller, the ionization probability will be smaller in those regions, ionization will hardly occur, and ionization will be concentrated at the emission site. Therefore, it is expected that the radiation angle ion current density will increase. The present invention was made based on this idea, and first, a sword-shaped member made of tan, Gesten (-V), iridium (Ir), etc. was used as the emitter chip, and the conventional surface diffusion method (heavily used) was first applied. The tip is made to protrude, and the entire surface is coated with zirconium (Zr).

It is coated with a metal having a smaller work function than the above-mentioned tungsten (1), iridium (Ir), etc., such as barium (13a), and then using the electric field method, the protrusion at the tip is formed, leaving only one core member at the base. That is, the retained material only at the emission site is removed. The emission sites thus formed effectively contribute to increasing the radiation angular ion current density.

Furthermore, if the coating phase, such as zirconium (Zr) or barium (1,33), remains as a monoatomic layer on the surface of the emitter chip after being subjected to electric field vaporization, the work function becomes even smaller, and selective ionization becomes even more difficult. promoted.

(6) Embodiments of the Invention Referring to the drawings, an emitter tip for a field ionized gas ion source according to an embodiment of the present invention will be explained below to clarify the structure and unique effects of the present invention.

As an example, a method for forming one mission site will be described when tungsten (W) is used as the emitter chip needle member and zirconium (Z[) is used as the coating material.

Refer to Figure 2 j Tungsten (W) with diameter of about 1.00 (l+m)
By electrolytically polishing one end of the needle-like part 4 411, the radius of curvature of the tip is about 2.000 (A),
Even beyond that! The crystal plane of 1mm is set as the (100) plane, heated to about 1,500 (K) in vacuum, and at the same time heated to 11:V.
/A) Each time an electric field is applied and the surface is diffused, a protruding tip 11' which is to be an emission site is formed.

See Figure 3 Metals with a smaller work function than tungsten (W), which is the material of the emitter tip, such as zirconium (
Zr) is coated over the entire emitter chip to form a zirconium (Zr) coating 21.

This step can be performed using a vacuum evaporation method or by dipping the emitter tip into a zirconium (Zr) melt.

Referring to FIG. 4, the electric field vaporization method is used to remove the Zr coating 21 formed on the tip 11'. At this time, the vapor 9j=TIi field of tungsten (W) is zirconium (Z
r) is larger than the evaporation electric field of tungsten ('W
) is not removed, but only zirconium (Zr) is selectively removed.

At this time, since the tip portion 11' has a very small curvature compared to the base portion IJ, the electric field strength increases and zirconium (Zr) in this region is evaporated by the electric field. Therefore, the tip 11
Even if the zirconium (Zr) coating 2t is completely removed, the coating 21 remains completely formed at the base. Therefore, the work function of the emitter tip is approximately 4.1 eV, which is the value of tungsten (, W ) at the tip 11', and 4.1 eV, which is the value of zirconium (Zr) at the base 11. (eV), ionization of gas molecules occurs intensively near the tip 11', and the radiation angular ion current density increases.

When the thickness of the residual zirconium (7,r) film at the base 11 becomes extremely thin, and in extreme cases becomes a monolayer, the work function becomes even smaller, 2.7 (e V).
It is even more effective.

In addition to the above-mentioned tungsten (W'), materials for the emitter tip include iridium (Ir), which has a work function power of about 5.3 rev), and zirconium (Zr) as the limb covering material. The work function of the pond is 2.5.
[Barium (13a), which has a voltage of about eV:l, can also be used to obtain the same effect.

Due to the height of the emitter tip, the electric field strength increases in the emission sensor due to its geometrical shape, and the ionization probability of gas molecules increases in other regions due to the difference in work function. As a result, intensive ionization at the emission site is promoted, and the combined effect of both of these capabilities makes it possible to see an emitter tube with a large radiation angular ion current density.

(7) Effects of the Invention As explained above, according to the present invention, the emission site of the emitter chip is limited to a specific area, and the electric field strength is large (i.e., the direct current density of C emitted ions is high). It is possible to provide an emitter chip for a field ionization gas ion source that can form a large ion source.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing an example of the basic structure of a field ionization gas ion source, and 211th to 4ν1 are -t
k is a sectional view of the emitter chip sales area after completion of the main steps in the method for forming an emission site of an emitter chip for a field ionized gas ion source according to an example; J... Vacuum container, 1'... Gas 34 population, 2... Counter electrode, 2'... For ion emission provided in the opposing mold part. Opening, 3...Emitter chip, 11...Base of the tip of the emitter chip, 11'...Tip that becomes the emission site of the emitter chip, 21... - Area coated with Zr. 12-

Claims (2)

[Claims] (1) An emitter chip for a field ionization gas ion source, characterized in that the work function of the member forming the tip is larger than the work function of the member forming the base. (2) The emitter chip for a field ionization gas ion source according to claim 1, wherein the member forming the tip portion is tungsten or iridium, and the member forming the base portion is silicone or barium.