JPH0544131B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for generating metal ions.

[Prior art and problems to be solved by the invention]

For example, ion generators are used for mass spectrometry and ion implantation of semiconductors. In any of these applications, it is desirable that the ion beam be narrowly focused and have a high density. Sources for generating such ion beams include (a) a small ion source size (b) a small ion energy range, (c) a large current, and (a) a small ion source size. It is necessary to have the following properties: (e) it has a long life, (e) it can ionize various metal substances, and (f) it has a clean mass spectrum (does not contain unnecessary mass spectra).

Therefore, some conventional ion generators will be considered. The following types are considered: (1) field ionization type, (2) field evaporation type, (3) surface ionization type, and (4) air discharge type.

(1) Field ionization type In this type, a strong electric field of 2 to 4 × 10 ⁸ [V/cm] is generated at the tip of a needle-shaped anode with a radius of curvature of several 1000 [Å], and neutral gas molecules incident on the anode are It ionizes. The advantages include a small ion source size, a small ion energy width, a long lifetime, and a clean mass spectrum. However, with this type, the substances that can be ionized are limited to specific gases,
The drawback is that the ionic current is extremely low at 10 ^-10 [A].

(2) Field evaporation type Similar to the field ionization type, 1×10 ⁸ to 1×10 ⁴ [V/
cm] is used to evaporate the anode material itself using a strong electric field. Also, the ion source is small, the energy width of the ions is small,
It has the advantage of being able to ionize various substances and providing a clean mass spectrum. However, it has the disadvantage that there are very few ion electrodes, and because the ionized substances are successively stripped off, the anode tip quickly becomes dull and has an extremely short lifespan.

(3) Surface ionization type This type ionizes a high-temperature metal surface with a high work function 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 space size is also extremely large.

(4) Air discharge type This is the most common type that ionizes through air discharge. Of the four examples above, this is the most suitable for drawing out a large current. However, the source size is large and the ion energy range is also large.
Another disadvantage is that the mass spectrum is not clear.

The results of these studies show that none of the conventional ion generators can satisfy all of the requirements.

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, and the ability to ionize various non-gaseous substances, especially metals. Moreover, the purpose is to provide an ion generator with a clean mass spectrum.

[Means to solve the problem]

For this purpose, in the present invention, the radius of curvature is
An anode is constructed by supplying a metal different from the needle electrode to a solid needle electrode with a 1000 Å tip by vapor deposition, surface diffusion, or impregnation, and the anode is heated to remove the supplied metal. Provided is an ion generator comprising a heater that provides thermal energy to facilitate movement, and a cathode that provides an electric field to ionize the atoms of the different metal between the anode and the anode in a vacuum atmosphere. It is.

[Embodiment] FIG. 1 shows the configuration of an apparatus according to the present invention, in which 1 is 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 has a heater power source 3
energized to heat 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 [Å]. This can be done by heating a needle-like anode whose tip has been polished to several hundred to several thousand angstroms by electric field polishing while applying a high voltage. 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. Therefore, a certain crystal face grows and bulges, and a protrusion (not shown) having a small radius of curvature of less than 100 [Å] is formed at the tip of the needle-like anode. The conditions for this protrusion to grow are based on the following equation.

F≒V/5r＞(8πγ/r)1/2 ...(1) where F: Electrostatic force applied to the tip of the needle electrode [V/cm] V: Relative potential difference between the anode and cathode [V] r: Needle Radius of curvature of needle-shaped anode [cm] γ: Surface tension of surface atoms of needle-shaped anode [dyne/cm] Taking tungsten as an example, F＞8.1×10 ⁴ r ^-1/2 [V/cm] ...( 2) Therefore, if r = 1000 [Å], V = 1.28
It is sufficient to apply a voltage of [KV] or more.
Then, if an anode temperature T and an electric field V which are higher than the values determined by the radius of the needle-shaped anode are 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≈V/5r, and the surface atoms of the protrusion acquire extremely large polarization energy and are ionized and desorbed. As a result, the radius of curvature of the protrusion remains 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 ionic current when the anode material itself is used as the ion species without adding a different metal to the needle-shaped anode in the device according to the present invention. In this case, the anode material, tungsten (310) W, is used as the ion species, and the radius of curvature of the tip of the needle electrode is
2000 [Å], and the degree of vacuum is 5×10 ^-8 [Torr]. 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 [°
K]. As a result, a substantially stable state is reached in about 10 minutes after applying thermal energy and electrostatic force. At this time, the supply of atoms to the protrusion and the ionization and desorption are in equilibrium.

In order to control the ion current with this device, it is sufficient to change the anode temperature or the applied voltage, and the current variable range can be obtained from 10 ^-11 to several μ [A], which is a sufficiently large current.

FIG. 3 shows the directional dependence of ions in the device according to the present invention. In this device, 2
It has a strong directionality, and in particular, one of them, A in the figure, has a stronger directionality, and B has a less strong directionality. The divergence angle of this A peak is 10 ^-2 [ster]. This is because, in principle, ions are emitted only from the protrusion of the anode, and the size of the ion source is also small, about less than 100 Å. 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, the mass spectrum is extremely clean, with Na ⁺ and K ⁺ being observed as impurities in the tungsten anode.

Further remaining among the aforementioned requirements are issues of lifetime and type of ionizable material. Of these, the lifespan depends on the value of the ion current taken out if atoms are not supplied.
If appropriate electric field and temperature are given, it is easy to obtain a period of several tens of hours or more. Substances that can be ionized include beryllium Be, boron B, aluminum A, silicon Si, titanium Ti, vanadium V,
Chromium Cr, iron Fe, cobalt Co, nickel Ni, copper
Cu, zinc Zn, germanium Ge, zirconium
Zr, neptunium Nb, molybdenum Mo, ruthenium Ru, rhodium Rh, palladium Pd, silver Ag,
Tin Sn, rhenium Re, osmium Os, iridium
There are a wide variety of materials, including Ir, platinum (Pt), gold (Au), etc.

In the above experimental example, the case where the needle-shaped electrode is made of a single type of metal and the constituent atoms of the needle-shaped anode are ionized as they are is shown. , by impregnation, etc. Further, the heater may be replaced by a laser beam or an electron bombardment, and its material may be made of tantalum Ta, carbon C, etc. other than 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.

〔Effect of the invention〕

As described above, the present invention supplies a metal different from the needle electrode to a solid needle electrode having a tip with a radius of curvature of several 1000 Å in a vacuum atmosphere by vapor deposition, surface diffusion, or impregnation. This constitutes the anode,
The anode is heated by a heater to provide thermal energy to facilitate the movement of the supplied metal, and the cathode provides an electric field between the anode and the anode to ionize atoms of the dissimilar metal.
Since almost all metals that can be used as needle electrodes can be used as anode materials, many types of metals can be ionized. And since it has a needle-like structure,
For example, the structure is significantly simpler and easier to manufacture than the conventional capillary type, and it consumes less power. Furthermore, compared to the capillary type, it is capable of ionizing elements with higher melting points, and is also superior in that the ion current can be controlled by temperature and voltage. Therefore, for mass spectrometry,
A device with extremely excellent performance can also be obtained for ion implantation.

[Brief explanation of the drawing]

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

Claims (1)

[Claims] 1. An anode constructed by supplying a solid needle-like electrode with a tip with a radius of curvature of several thousand amps with a metal different from that of the needle-like electrode through vapor deposition, surface treatment, and impregnation. , a heater that provides thermal energy to heat the anode to facilitate the movement of the supplied metal, and a cathode that provides an electric field to ionize atoms of the dissimilar metal between the anode and the anode in a vacuum atmosphere. Ion generator provided.