JPH0261941A - Electric field dissociative ion source - Google Patents

Abstract

PURPOSE:To provide a stable ion source of electric field dissociated type having a high brightness by inclining a gas lead-in path a certain angle to an emitter, and locating the tip of the emitter on an extension line of the lead-in path. CONSTITUTION:An emitter 1 consisting of needle-shaped tungsten is fixed to a hole provided on the center axis of a columnar emitter holder 5. This emitter holder 5 is equipped with a gas lead-in path 3, for example, in a circular profile. This gas lead-in path 3 is composed of a portion in parallel with the emitter 1 and another portion inclined an angle theta (e.g., 45 deg.) to the emitter 1, and the tip of the emitter 1 is located on an extension line of this inclined portion. From this lead-in path 3 such an ion source gas is supplied as helium and hydrogen. Thus, the gas molecular density in the neighborhood of the tip of the emitter is raised without causing electric discharge, and a high density, stable ion source of electric field dissociated type is accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a field ion source, and is suitable for use in, for example, a focused ion beam device.

[Summary of the invention]

The present invention provides a field ionization type ion source using a gas as an ion source, in which the gas introduction path is inclined at a predetermined angle θ (however, θ≠0°) with respect to the emitter, and is located on an extension line of the introduction path. The tip of the emitter is located above. This makes it possible to realize a field ionization type ion source with high brightness and stability.

[Conventional technology]

A field ion source that uses gas as an ion source is used, for example, as an ion source for a focused ion beam device (for example, Japanese Patent Laid-Open No. 117122/1983). One way to increase the ion current emitted from this field ion source is to increase the gas molecule density of the ion source gas near the tip of the emitter. However, since a high voltage of several to several tens of kV is normally applied to the emitter, simply attempting to increase the gas pressure will cause discharge and the emitter will no longer function as an ion source.

FIG. 7 shows a conventional field ionization type ion source.

As shown in FIG. 7, in this conventional field ion source, an emitter 101 is surrounded by a metal cover 102, and the ion source gas is supplied to the cover 102.
be introduced inside. Reference numeral 103 indicates an aperture for extracting the ion beam. Since the ion source gas introduced into the interior of the cover 102 leaks to the outside only through this aberration 103, the gas pressure inside the cover 102 can be kept high and the gas pressure outside can be kept low. If the diameter of the aperture 103 is made smaller, the cover 10
Although the ratio of the gas pressure inside the cover 102 to the gas pressure outside the cover 102 can be increased, the lower limit of the diameter of the aperture 103 is determined by the position of the tip of the emitter 101 and the aperture 103 when assembling the ion source. Limited by alignment accuracy. Therefore, this aperture 1
The diameter of 03 is usually limited to a few inches. In FIG. 7, reference numeral 104 is an emitter holder, reference numeral 105 is a sapphire block, reference numerals 106 and 107 are members provided with gas passages, reference numeral 10 is a cold head cooled with liquid nitrogen, and reference numeral 109 is an ion A gas introduction pipe for introducing source gas is shown.

FIG. 8 shows a field ion source previously proposed by the present inventors. As shown in FIG. 8, this field ion source has an emitter 1 in a nozzle 110 made of alumina.
Since the structure is such that the nozzle 110 is inserted, the inner diameter of the nozzle 110 can be reduced to about several hundred μm. Therefore, the density of gas molecules near the tip of the emitter 101 can be increased, and the amount of gas leaking to the outside from this nozzle 110 can be reduced. In addition, the 8th
In the figure, reference numeral 111 indicates a member provided integrally with the nozzle 110, reference numeral 112 indicates a member having a gas introduction pipe 112a, and reference numeral 113 indicates an O-ring.

[Problem to be solved by the invention]

Emitter 1 in the field ion source shown in Figure 8
Figure 9 shows the results of analyzing the gas molecule density distribution near the tip of 01. In FIG. 9, changes in the gas pressure distribution with respect to the distance X from the tip of the emitter 101 are shown. As is clear from FIG. 9, the gas pressure and therefore the gas molecule density are lower near the tip of the emitter 101 than in the surrounding area.

In this way, the conventional field ionization type ion source shown in FIG. 8 has a low density of gas molecules near the tip of the emitter 101.
Therefore, the brightness of the ion source was insufficient.

Therefore, an object of the present invention is to provide a high-intensity and stable field ionization type ion source.

[Means to solve the problem]

According to the inventor's study, the reason why the density of gas molecules near the tip of the emitter 101 in the field ion source shown in FIG. Since they match,
The problem is that the conical tip of the emitter 101 is in the shadow of the handle. Therefore, in order to increase the density of gas molecules near the tip of the emitter 101, it is necessary to prevent the tip of the emitter 101 from being in the shadow of the handle so that the ion source gas can be efficiently supplied to the tip of the emitter 101. do it.

The present invention has been devised based on the above considerations.

That is, in order to solve the above problems, the present invention provides a field ionization type ion source that uses gas as an ion source, in which the gas introduction path (3) is set at a predetermined angle θ (however, θ≠ 0°) inclined, and the introduction path (3
) The tip of the emitter (1) is located on an extension of the line.

The angle θ can be set to various angles other than 0°. However, if this angle θ is larger than 90°, the electric field near the tip of the emitter (1) will weaken due to the presence of a nozzle forming the gas introduction path (3), and the emitter (
Some of the ions emitted from 1) enter this gas introduction path (3
) is irradiated to the nozzle forming the irradiation, which may generate secondary electrons or cause charge-up in the nozzle, etc., so it is preferable that the angle θ is 90″ or less.

In a preferred embodiment of the present invention, as shown in FIG.
is placed. This nozzle 2 forms a gas introduction path 3. The ion source gas is supplied to the tip of the emitter 1 through this gas introduction path 3. In addition, θ-90@
The case is shown in Figure 3.

[Effect]

According to the above-mentioned means, the ion source gas is
-It can be efficiently supplied to the tip of (1).
The density of gas molecules near the tip of this emitter (1) can be increased. This makes it possible to increase the brightness of the field ion source. With L7, the occurrence of discharge is also suppressed, and the stability of this field ionization type ion source is good.

FIG. 4 shows the dependence of the gas molecule density at the tip of the emitter on the ion source structure, and shows the ion source shown in FIG.
The results of a computer analysis of the gas molecule density at the tip of the emitter are shown for the ion source shown in FIG. 6, which is a model of the conventional field ion source shown in FIG.

The horizontal axis in FIG. 4 is the inner diameter DN of the nozzle 2 shown in FIG. 5, and the vertical axis is the gas molecule density N at the tip of the emitter 101 shown in FIG. to the gas molecule density N at the tip of the emitter 1 shown in FIG. 5, N,/Ns. In FIG. 4, the distance LKN between the tip of the nozzle 2 and the tip of the emitter 1 shown in FIG. 5 is used as a parameter. In addition, in FIG. 5, the diameter d of emitter 1 is 120
μm, length of the conical part at the tip of emitter 1 = 300
am, the distance L' between the tip of the nozzle 2 and the gas molecule generation region 4 at the bottom of this nozzle 2 is 1000 μm,
In FIG. 6, the diameter d of the emitter 101 is 120 μm,
Length 1 of the conical part at the tip of emitter 101 = 300 μm
, inner diameter DNO of the nozzle 110 = 500 pm, distance L between the tip of the nozzle 110 and the gas molecule generation region 114
'=20m, emitter 10 from the tip of nozzle 110
The protrusion length of 1 is 200 μm. Further, it was assumed that gas molecules are uniformly generated from the above gas molecule generation region 4.114, and that the number of gas molecules generated is also the same. Gas molecule density N s , N s . The measurement of emitter 1
．． The measurement was carried out by counting the number of gas molecules incident on the tip of the emitter 1.101 using a spherical gas detector S with a radius of 50 μm provided at the tip of the emitter 1.101.

As is clear from FIG. 4, the smaller the inner diameter DN of the nozzle 2 shown in FIG. 5, and the smaller the distance LEN between the tip of the nozzle 2 and the tip of the emitter I, the smaller the gas molecular density ratio N s / N. s. becomes higher.

When considering the case of actually manufacturing an ion source, the accuracy of aligning the tip of emitter 1 on the extension line of nozzle 2 is 100.
If the limit at which the tip of emitter 1 must protrude beyond the tip of nozzle 2 is about 100 μm, then
Inner diameter of nozzle 2.

It is thought that the distance LEN between the tip of the nozzle 2 and the tip of the emitter 1 is about 350 μm, and the gas molecular density ratio N s / N at that time is about 100 μm.
s. is 7.4.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a field ion source according to one embodiment of the present invention.

In FIG. 1, reference numeral 1 indicates a needle-shaped emitter made of tungsten (W), for example, and reference numeral 5 indicates a cylindrical emitter holder, for example. Since the ion source needs to be cooled to an extremely low temperature, a material with high thermal conductivity and easy processing is used for the emitter holder 5, and specifically, sapphire, for example, is used. The emitter 1 is fixed in a hole provided on the central axis of the emitter holder 5. Further, this emitter holder 5 is provided with a gas introduction path 3 having, for example, a circular cross-sectional shape. This gas introduction path 3 consists of a portion parallel to the emitter 1 and a portion inclined at an angle θ (for example, 45°) with respect to the emitter 1, and the tip of the emitter 1 is located on an extension of this inclined portion. and,
For example, helium (He) or hydrogen (
An ion source gas such as Hz) is supplied.

According to this embodiment, the gas introduction path 3 is inclined at an angle θ with respect to the emitter 1 as described above, and this gas introduction path 3
Since the tip of emitter 1 is located on the extension line of
The ion source gas can be efficiently supplied to the tip of the emitter 1, and therefore the gas molecule density of the ion source gas near the tip of the emitter 1 can be increased.

Therefore, it is possible to increase the brightness of the ion source. Furthermore, the occurrence of discharge and the like is small, and the stability of the ion source is excellent. This makes it possible to realize a field ionization type ion source with high brightness and stability. Furthermore, emitter 1
Since the ion source and the gas introduction path 3 are integrally constructed, the ion source is easier to assemble and handle than when the ion source is constructed by combining separate emitters and nozzles.

The field ionization type ion source according to this embodiment can be used, for example, as an ion source for a focused ion beam device, and is used, for example, when performing ion beam writing on a semiconductor wafer. The focused ion beam apparatus using the high-performance field ion source according to this embodiment allows microfabrication using an ion beam, exposure of a resist, and analysis of a microscopic region.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the technical idea of the present invention.

For example, the cross-sectional shape of the gas introduction passage 3 in the above-described embodiment may be a shape other than circular;
may be provided in plural numbers as necessary. Furthermore, it is also possible to use a gas introduction path having the shape of a rotating body obtained by rotating the cross-sectional shape of the gas introduction path 3 shown in FIG. 1 around the central axis of the emitter holder 4.

[Effects of the Invention] As described above, according to the present invention, the ion source gas introduction path is formed at a predetermined angle θ (however,
θ≠0), and the tip of the emitter is located on the extension line of the gas introduction path, so it is possible to increase the density of gas molecules near the tip of the emitter without causing discharge, resulting in high brightness. A stable and stable field ion source can be realized.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a field ion source according to an embodiment of the present invention, and FIG. Figure 3 is a cross-sectional view of the field ion source with the angle θ = 90° in Figure 2, Figure 4 is a graph showing the dependence of the gas molecule density at the tip of the emitter on the ion source structure, and Figure 5 is a graph showing the structure of the ion source. FIG. 6 is a diagram showing a structural evaluation model of a conventional field ion source; FIG. 7 is a cross-sectional view of a conventional field ion source; FIG. 8 is a sectional view showing another example of a conventional field ion source, and FIG. 9 is a diagram showing a gas pressure distribution near the tip of the emitter of the field ion source shown in FIG. Explanation of main symbols in the drawings 1: Emitter 2: Nozzle 3: Gas introduction path.

Claims (1)

[Claims] In a field ionization type ion source using a gas as an ion source, the introduction path for the gas is formed at a predetermined angle θ (
However, the field ion source is characterized in that the emitter is inclined (θ≠0°) and the tip of the emitter is located on an extension of the introduction path.