JPS5885242A - Dotted ion source - Google Patents

Abstract

PURPOSE:To radiate an ion beam of high intensity in the axial direction by rounding a pin-shaped tip electrode for ionization and providing on its top, a minute projection with specific top radius of curvature and height. CONSTITUTION:A dotted ion source used in an ion microanalyzer or the like is formed so that decompressed gas can be supplied to a pin-shaped tip electrode 1 in which positive high voltage is applied to an opposed electrode 2 and the gas can be ionized by the actuation of the high elelctric field that exists in the vicinity of the electrode surface. In this case, a minute projection with the height h and top radius of curvature r that satisfy 5Angstrom <h<2mum and R/100<=r< R/2 is provided on top of the pin-shaped chip electrode 1 with the top average radius of curvature R. As a result, an ion beam radiation angle can be restricted to a narrow area and the intensity of beam radiation current can be increased and then an ion beam of high intensity exceeding several times as high as the ion beam can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a point ion source useful in ion beam application equipment such as ion microanalyzers.

As an ion source that emits a narrow, high-intensity ion beam,
A point ion source that utilizes the electric field ionization phenomenon is known. As shown in FIG.
This method involves supplying gas at a moderately reduced pressure and ionizing this gas by the action of a high electric field that exists near the surface of the needle-shaped tip electrode. The tip of the needle tip is generally close to a spherical surface with a radius of curvature of the tip, and the high electric field is almost uniform near the spherical surface. For this reason, the supply gas is uniformly ionized on the spherical surface, and is therefore emitted from the needle tip over a wide aperture angle range, generally about 1 to 2 rad. However, what is actually used in ion beam application equipment such as ion microanalyzers is an ion beam that passes through a fine aperture hole and is emitted in a narrow range of less than 1 rad from a needle-like tip. More than 90% of the emitted ions are wasted.

This unused ion beam collides with the wall near the electrode, but at this time it generates harmful secondary electrons, which is an obstacle to stable operation of the ion source. As a practical point ion source, it is desirable to emit ions at a narrow opening angle in the axial direction of the needle tip.

The present invention has been made in view of this point, and an object of the present invention is to provide a point-like ion source that effectively emits a high-intensity ion beam in the axial direction of a needle-like tip. The present invention will be explained in detail below.

The point ion source used in the present invention utilizes the electric field ionization phenomenon. Field ionization occurs preferentially in areas where the electric field is large near the surface of the needle tip. Therefore, in order to emit a strong ion beam in the axial direction of the needle tip, it is necessary to devise ways to increase the electric field preferentially near the apex of the needle tip. The electric field near the needle tip surface is determined by the geometry of the needle tip surface.

The electric field becomes large near the protruding portion with a small radius of curvature. Therefore, if a minute protrusion is provided at the top of a needle-like tip with a uniform tip curvature, ionization will occur preferentially at this protrusion, and the ion beam will be emitted effectively in the axial direction of the needle-like tip. That will happen. FIG. 2 shows a comparison between a conventional needle-like tip and a needle-like tip according to the present invention, where (a) is the conventional needle-like tip and Φ) is the needle-like tip according to the present invention. The desirable relationship between the tip curvature radius (R) of the microprotrusion and the average radius of curvature (R) of the needle tip is as follows:
If *'<R/100, it is difficult to create microprotrusions, and it is also physically unstable and easily destroyed by ion collisions or reactions with gas, making it impractical. On the other hand, r>R/
In case 2, the effect of electric field concentration due to the microprotrusions is small.

The height h of the microprotrusion is 5λ×h and the yoke of 2 μm is xtt, h. If h is less than 5 Å, the protrusions tend to disappear; if h is less than 2 μm, the protrusions do not have enough strength and are broken in a strong electric field.

There are many methods for forming such microprotrusions.

For example, a method that utilizes the phenomenon (build-up phenomenon) in which a specific crystal plane of the needle-shaped tip rises by MB by heating the needle-shaped tip and applying a high voltage while it is in a round state, or attaching the material by vapor deposition, spunter, etc. The precipitates can be removed by using the difference in polishing speed between the base material and the precipitates when processing the needle-like tip material into a needle shape by electrolytic polishing, etc., using a material containing fine precipitates. A method of exposing it as a protrusion on the surface of a needle-like chip.

Furthermore, a method may be used in which the precipitate is exposed as a protrusion by electric field evaporation of the needle tip by utilizing the difference in field evaporation intensity between the base material and the precipitate. Although the microprotrusions produced by these methods rarely exhibit the typical KFi smooth R surface shape, they can be used satisfactorily in general ion beam application equipment. If a smooth spherical protrusion is particularly desired, the shape of the protrusion can be modified using high-temperature annealing of a needle tip or field evaporation.

The acicular tip provided with microprotrusions according to the present invention not only has the effect of limiting the radiation direction of the ion beam to a narrow opening angle as described above, but also has the great practical effect of increasing the brightness of the ion beam. There is.

In an ion source that uses electric field ionization, the gas to be ionized is supplied not only by colliding with the needle tip from the atmosphere outside the needle tip, but also by gas adsorbed on the surface of the shaft of the needle tip along the axis. It can also be achieved by diffusing toward the tip of the needle tip to reach the tip. The latter effect becomes noticeable in a region where the temperature of the needle tip and the gas is close to the liquefaction temperature of the gas. In the case of a needle-like tip provided with microprotrusions S, it is adsorbed to the needle-like tape,
Most of the gas that has diffused to the tip is ionized at the minute protrusions, which improves the brightness of the ion beam. A needle-like tip provided with microprotrusions can produce an ion beam with several times higher brightness than a conventional needle-like tip.

As described above, a point ion source using a needle-like tip provided with minute protrusions has the great practical effect of narrowing the radiation angle of the ion beam and improving the brightness at the same time.

The present invention will be explained below according to examples.

Example 1 A W needle-like tip with a tip curvature radius of about 1000 in the <100> direction was heated to a temperature of 1400 to 2000 C' in an oxygen atmosphere of 10' to 10'''''l'o r r.
A high voltage was applied to build up the (100) plane of the tip of the W needle-like tip to form a microprotrusion. When the shape of the microprotrusion was observed using a high-resolution f-type scanning electron microscope, it was found that the tip radius of curvature was approximately 200 mm and the height was 500 mm.

This W needle-shaped tip with microprotrusions formed thereon is used as a point ion source and mounted on the ion beam optical system shown in Fig. 1.
Cool the W needle tip to 20K.

A hydrogen ion beam was generated by supplying hydrogen gas cooled to the same temperature. The radiation angle of the hydrogen ion beam was reduced to about one-tenth of that without the microprotrusions. The radiation current density of the hydrogen ion beam also increased by 50%.

Mei1ffA Example 2 (111> azimuth radius of tip curvature 2000 people Ir needle f'') 10-krorr in vacuum Te 1500~
A high voltage was applied while heating to 18oC, and microprotrusions were formed on the surface of the Ir needle-like chip using a build-up i-type. The tip radius of curvature of the protrusion was approximately 500, and the height was 20.

When this needle-like tip was used as a nitrogen and oxygen gas ion source, the ion beam radiation angle was reduced to less than a fraction of a fraction of that in both cases, and the ion beam radiation current density was improved by more than 100%.

Example 3 Hexaboride M Bs s (M = C"tB'#B" with a tip curvature radius of about 1000 A in the <100> direction
eL"rc"rP'Nd, 8m, Eu) After forming the tip of the needle-like tip into a uniform spherical surface by the high electric field method, it was heated to 1700 to 21cm in a 10-'TOrrO vacuum.
The metal element M on the surface was preferentially evaporated by heating at a degree of 00C to form B-rich island protrusions on the surface of the needle tip. This island-like protrusion has a tip curvature radius r of 50 (r
(800A, Mh is 5<j)<20OA and it is 6.

After confirming the position of this island-like protrusion using a field ion microscope, adjust the position so that this protrusion is on the axis of the ion beam optical system.
It was installed in the device shown in Figure 1.

When NetAr* gas was ionized using the needle tip, the radiation angle of the ion beam was reduced.

A remarkable effect was observed in improving the ion beam radiation current density.

Example 4 A heat-treated Fe-Mo-C alloy was used as the needle-shaped chip material. It was confirmed by electron microscopy that this sample contained fine Mo and C grains. In the process of processing the sample into a needle shape by electric wI polishing, Fe-MO-C
By utilizing the difference in polishing speed between the alloy matrix and the MOIC particles, MO and C particles were made to protrude from the surface of the needle-like tip. Continuing,
MO*C particles were processed to have a uniform radius of curvature at the tip by field evaporation to form microprotrusions of Mo t C. The size of the MO, C protrusion with the needle-like tip Kjl was 500 A in radius of curvature and 30 in height.

The average tip curvature radius of this needle tip was 2000A.

This needle-shaped tip was used as a point ion source for generating Nt, Xe, and l(e gas ions.

Significant desirable effects were observed in reducing the ion beam radiation angle and improving the ion beam radiation current density.

Example 5 A Be needle tip with a tip curvature radius of 1600 in the <0001> direction was formed into a spherical surface by field evaporation, and then Ret-evaporation was performed from just above the needle tip in the axial direction (Be on the 00011 plane). The process of He burial was observed using a field ion microscope or a field electron emission microscope.

If too much Re is deposited and it is not deposited on the desired crystal plane, the buried RC is removed again by field evaporation and Be evaporation is repeated until the desired deposit is obtained. Ta. By this method, a deer le of about 300 mm in diameter and 200 mm in height was placed on the top of the Re needle tip with a tip radius of about 1600 mm
e was deposited. Heating this needle tip at high temperature, ss
At the same time, the ShikuHe was blended with the base, and at the same time, it was formed into a microprotrusion with a radius of curvature of 150 mm at the tip and a height of 100 mm by diffusion on the second surface.

This needle tip was transferred to CH, BH Lu, Ret4. PHI
.

When PCt・e H+A' gas was used to ionize, the emission angle of the ion beam was less than a fraction of that when no microprotrusions were provided, and the emission current density was FiSO~100.
% improvement was confirmed.

In the above embodiment, a case was described in which Be was vapor-deposited on the H, E needle-like tip, but it goes without saying that the same effect can be obtained even if the material of the needle-like chip and the material to be vapor-deposited are different. For example, I r , Pt on a Be needle tip
+Rh +W, Mo +T i IC, etc. may be deposited.

As described in the above embodiments, by providing a microprotrusion at the tip of the needle tip, if the ion beam radiation angle of the point ion source is limited to a narrow area, the radiation current will be equal to 4 times the ion and 1 time. Density is improved. Furthermore, the needle-shaped tip having this shape can be easily manufactured as described in the above embodiment. Therefore.

The present invention is practically useful for improving the performance of ion beam application equipment.

[Brief explanation of the drawing]

Figure 1 shows a point ion source that utilizes electric field ionization, and Figure 2 (a) shows the tip of a conventional needle-like tip.
FIG. 2 is a diagram showing the shape of the tip of a needle-like tip according to the present invention. 1... Needle-shaped tip electrode, 2... Counter electrode, 3...
Gas leak pulp, 4... Gas cylinder, 5... Ion beam lens, 6... Ion beam. 1st liZ (d) (b)

Claims (1)

[Claims] In a point ion source that ionizes gas by electric field ionization, at the tip of a needle-like tip electrode for ionization whose tip has an average radius of curvature of approximately. A point ion source characterized by having a rope of 5 x 2 μm and a minute protrusion with a radius r at the tip.