JPS5833649B2 - ion generator - Google Patents

Description

[Detailed description of the invention] The present invention relates to an apparatus for generating an ion beam.

For example, ion generators are used for mass spectrometry and ion implantation of semiconductors.

Even in these applications, it is desirable that the ion beam be narrowly focused and at a high density.

As a source for generating such an ion beam, (a) the ion source size (size of the ion source) is small;

(b) The energy range of ions is small. (c) Large current can be obtained.

) have a long lifespan. (e) Various substances including metals can be ionized.

(to) The mass spectrum is clean (does not contain unnecessary mass spectra).

It is necessary to have the following characteristics.

Therefore, some conventional ion generators will be considered.

The following types are considered: (1) field ionization type, (2) field evaporation type, (three-sided ionization type), and (4) air discharge type.

(1) Electric field ionization type This is caused by a strong electric field of 2 to 4 x 103 [■/crrL] generated at the tip of a needle-like anode with a radius of curvature of several 100C.
Neutral gas molecules incident on the anode are ionized by an electric field.

The advantages include a small ion source size, a small ion energy width, a long lifetime, and a clean mass spectrum.

However, this type of device has the disadvantage that the substances that can be ionized are limited to specific gases, and the ion current is extremely small at io''-t° [A].

(2) Similar to the field evaporation type and field ionization type, 1×103 to 1×104 [■/Crr
The anode material itself is evaporated by the strong electric field L].

Its advantages include a small ion source, a narrow ion energy width, the ability to ionize various substances, and a clean mass spectrum.

However, the drawback is that the ion current is extremely small, and the ionized material is stripped off one after another, so the anode tip quickly dulls and has an extremely short lifespan.

(3) Surface ionization type In this type, the surface of a metal with a high work function heated to high temperature is ionized by spraying the vapor of an element with low ionization energy, such as an alkali metal.

Its advantages include a small ion energy width and a clean mass spectrum.

However, there are disadvantages in that the materials that can be used are extremely limited and the source size is also extremely large.

(4) Air discharge type This is the most common type of ionization using air discharge.

Of the four examples above, this is the most suitable for drawing out a large current.

However, the source size is large, the ion energy range is wide, and the mass spectrum is not clear.

From these study results, it can be seen that the conventional ion generator cannot satisfy all the requirements for collapsing.

The present invention has been made in view of the above points, and has a small ion source size, a narrow ion energy width, a large current, a long life, the ability to ionize various substances, and a clean mass spectrum. The purpose is to provide an ion generator.

To achieve this objective, the present invention provides a needle-shaped anode formed of a substance to be ionized and has a sufficiently small radius of curvature, and heats this anode in vacuum to a temperature above the melting point of the substance to be ionized. At the same time, by applying a high electric field between the anode and the cathode, it is configured as an ion generator that electrohydrodynamically ionizes and detaches surface atoms from the tip of the anode.

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

FIG. 1 shows the configuration of an apparatus according to the present invention. Reference numeral 1 denotes a needle-shaped anode made of tungsten or the like, which is attached to a heater 2 made of tungsten or the like.

This heater 2 is energized by a heater power source 3 and heats the needle-like anode 1 .

On the other hand, a cathode 5 is provided to face the acicular anode 1 , and a high electric field is applied between the cathode 5 and the acicular anode 1 by a high voltage power source 4 .

The needle-shaped anode 1 is configured so that its source size is less than 100 [in].

For this purpose, electrolytic polishing is used to polish the tip to several 100 to several 100
It is sufficient to apply a high voltage to a needle-shaped anode polished to 0C and heat it.

In this case, the work function, surface energy, local electric field, etc. of each crystal plane at the tip of the needle electrode are different.

For this reason, a certain crystal face grows and bulges, and a protrusion (not shown) having a small radius of curvature of less than 100 degrees is formed at the tip of the needle-like anode.

The conditions for the growth of this protrusion are based on the following equation.

FF=■15r〉(8πr/r)'/” =-=・(
1) However, F: Electrostatic force applied to the tip of the needle electrode [■/
cIrL] V: Relative potential difference between anode and cathode (V) r: Radius of curvature of needle-shaped anode [dynamic] r: Surface tension of atoms on the surface of needle-shaped anode Cdyne /CrfL) Taking tungsten as an example, F>8 ．． I X 10'r-'/"CV/Cm) -
” (2), so r = 1000C people], then ■
It is sufficient to apply a voltage of =1.28 (KV) or more.

Then, if an anode temperature T1 electric field (2) higher than a value determined by the radius of the needle-shaped anode is applied, the radius of curvature r of the protruding portion of the anode tip decreases over time.

Along with this, F increases due to the relationship F≠V15 r,
The surface atoms of the protrusions acquire extremely large polarization energy and are ionized and desorbed.

As a result, the radius of curvature of the protrusion is kept at a constant value and is in an equilibrium state.

That is, in the protrusion, the supply of atoms to the protrusion due to thermal energy and electrostatic force and the reduction of atoms due to ionization and desorption are perfectly balanced, and an extremely stable ion current is continuously obtained.

FIG. 2 shows the temporal change characteristics of the ion current in the device according to the present invention.

In this case, the ionic species is tungsten, i.e. (3
10) Using W, the radius of curvature of the tip of the needle electrode was 2000 C], and the degree of vacuum was 5 x 10-8 (Tor
r).

Then, thermal energy and electrostatic force were applied simultaneously to the needle electrode, increasing the anode potential to 5 (KV) and the temperature to 1800 C'K).
Make it.

As a result, a substantially stable state is reached in about 10 minutes after the application of thermal energy and electrostatic force.

At this time, the supply of atoms to the protrusion and the ionization and desorption are in equilibrium.

With this device, the ion current can be controlled by changing the anode temperature or applied voltage, and the current variable range is 10-11.
~ several μ[A] is a sufficiently large current.

FIG. 3 shows the directional dependence of ions in the device according to the present invention.

This device has strong directionality in two directions, especially the one of them, A has stronger directionality in the figure, and B has less strong directionality.

The divergence angle of this human peak is 10-'' (5ter).

This is because, in principle, ions are emitted only from the protrusion of the anode, and the thickness of the ion source is also small, about less than 100 mm.

In addition, the energy width of the ions is 1 (eV) or less, which satisfies the requirements.

FIG. 4 shows the mass spectrum of ions in the apparatus according to the present invention.

As is clear from the figure, in addition to W+ ions, Na+, K
It has a blessedly clean mass spectrum, with + being observed as an impurity in the tungsten anode.

Further remaining among the aforementioned requirements are issues of lifetime and type of ionizable material.

Among these, as for the lifespan, when no atoms are supplied, it is easy to obtain several tens of hours or more if an appropriate electric field and temperature are given, although it depends on the value of the ion current taken out.

In addition, substances that can be ionized are beryllium Be, boron B
1 Aluminum At, Silicon Si1 Titanium Ti1
Vanadium v1 Chromium Cr, Iron Fe, Cobalt Co,
Nickel Ni.

Copper Cu, Zinc Zn, Germanium Ge1 Zirconium Zr, Neptunium Nb, Molybdenum Mo.

Ruthenium Ru, rhodium Rh, palladium Pd.

Silver Ag, Tin Sn1 Rhenium Re, Osmium Os.

There are a wide variety of materials, including iridium Ir, platinum Pt, gold Au, etc.

In the above embodiment, the needle electrode is made of a single metal,
Although the case where the constituent atoms of the acicular anode are ionized as they are is shown, the acicular anode may be supplied with elements of the same or different type as the anode by vapor deposition, surface diffusion, impregnation, etc.

Further, the heater may be replaced with a laser beam or an electron beam, and its material may be made of tantalum Ta, carbon C, etc. in place of tungsten.

Furthermore, although the power source for applying a high electric field between the anode and the cathode is inserted between the anode and the ground, it may be inserted between the anode and the cathode.

As described above, the present invention includes a needle-like anode formed of a substance to be ionized and having a sufficiently small tip with a sufficiently small radius of curvature, and a heater that applies thermal energy to the anode to raise the temperature of the substance above its melting point. It is possible to provide a device that satisfies all the requirements that an ion generator should have, since it is equipped with a cathode that applies a high electric field, and the surface atoms of the needle-like anode are electrohydrodynamically moved to ionize and desorb from the tip. can.

Therefore, an apparatus with extremely excellent performance can be obtained both for mass spectrometry and for ion implantation.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the electrical configuration of the device according to the present invention,
Figure 2 is a diagram showing the temporal change characteristics of the ionization current in the same device, Figure 3 is a diagram showing the directional dependence of ions in the same device, and Figure 4 is an explanatory diagram of the mass spectrum in the same device. It is. 1... Needle electrode, 2... Heater, 3, 4... Power supply, 5... Cathode.

Claims (1)

[Claims] 1. A needle-like anode having a tip formed of a substance to be ionized with a radius of curvature smaller than several thousand centimeters;
An electric field is provided between the anode and the anode and a heater that provides thermal energy to heat the anode to a temperature higher than the melting point of the substance and ionize the surface atoms of the tip. An ion generator that has a cathode and a cathode in a vacuum atmosphere.