JPS5944751A - Ion source - Google Patents

Abstract

PURPOSE:To generate stable ion beam for a long period of time by providing a heating means which heats a reservoir to which substance to be ionized is reserved, a pair of leadout electrodes attached to the end of reservoir and a means for causing electron beams to collide with the end of reservoir. CONSTITUTION:A heater 12 is uniformly wound around a reservoir 1 in which substance 4 to be ionized is reserved and the heater 12 is heated by a power source 13. A temperature of reservoir 1 is measured, for example, by a thermocouple 14 and a voltmeter 15 and is kept at the specified value in accordance with a kind of substance 4 through the feedback to the power source 13. A plug 16 hermetically seals the reservoir 1, except for a fine hole 3. When the temperature reservoir 1 reaches the preset value, an acceleration voltage and leadout voltage are applied to each electrode from the acceleration voltage source 10 and leadout voltage source 11 and moreover the filament 7 is heated by the filament voltage source not shown in the figure. Thereby, the end 2 of reservoir 1 is excited by electrons. The electron beam generated from the filament 7 is concentrated to the end portion 2 and thereby the ion beam in a heavy current can be stably obtained at the leadout electrode 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal ion source, and particularly to an ion source that can generate a stable ion beam for a long period of time.

Figure 1 shows a conventional metal ion source, in which reference numeral 1 is made of metal such as tantalum or tungsten, the tip 2 has a 0.1 mm pore 3, and the inside contains, for example, iodide. [The ionized substance 4, such as lithium, is stored in an arbor. 5 is placed opposite the tip 2 of the reservoir 1 and is kept at a negative potential with respect to the reservoir 1;
This is an extraction electrode having an opening 6. Reference numeral 7 denotes a spiral filament disposed on the side of the extraction electrode 5 opposite to the reservoir 1. Reference numeral 8 denotes an acceleration electrode set to a ground potential for accelerating the ion beam I13, and a diaphragm plate 9 is fixed to the electrode 8 to limit the exit angle of the ion beam IB (7). 10 is an acceleration power source that applies a high voltage VI to the beam ff-bar 1; 11 is an extraction power source that applies an extraction voltage V2 between the beam 1 arbor 1 and the extraction electrode 5;

In the configuration as described above, the reservoir 1 is filled with an ionized substance 4, such as, for example, sium iodide. Here, the potential difference (V+-V
2) is set to several hundred volts, for example, and the influence of the electric field due to the positive potential of the reservoir 1 extends to the filament side through the opening 6 of the extraction electrode 5.
The electric field around the tip is concentrated near the tapered tip 2.

As a result, when the filament 7 is heated by a heating source (not shown), the electrons generated from the filament 7 are focused by the electric field between the reservoir 1 and the extraction electrode 5, are further accelerated, and collide with the tip 2 where the electric field is concentrated. Heat the perilla part. This causes the temperature of the ionized substance 4 in the reservoir 1 to rise and melt. Then, a part of it flows out through the pore 3 to the tip 2 of the reservoir 1 . The ionized substance liquid that has reached the tip 2 of the reservoir 1 maintains a balance between the electrostatic horn caused by the electric field generated by the voltage applied between the reservoir 1 and the extraction electrode 5 and the surface tension of the liquid itself. It becomes a shape. Here, the so-called Pula cone (
It forms a cone called a Taylor cone.
At its tip, the ionized substance 4 is heated and evaporated,
The ion beam collides with electrons and becomes ions, and is further accelerated by the accelerating electrode 8 and extracted as an ion beam IB.

By the way, in the conventional device shown in FIG.
The heating and ionization of the reservoir 1 was caused by the electron collisions caused by the filament 7, and it was difficult to heat the reservoir 1 sufficiently.
If the reservoir has a small volume, it can be heated relatively easily, but in order to extend the usable time of the ion source, it is preferable to use a reservoir with a large volume.

In addition, the average heating of the reservoir 1 (uniform depletion r i The vaporized ionized substance 4 is liquefied, liquefied, and further vaporized and released from the hole 3 of the ionized substance 4. On the other hand, a part of the vapor of the vaporized ionized substance 4 moves into the space of the reservoir 1.F. Since the temperature at the top of the arm 1 is lower than the melting point of the ionized substance 4, some of the vapor condenses and adheres to the inner wall of the reservoir 1. If the ion source is not operated for a long time in this state, this condensation will continue. This leads to the formation of a thick recrystallized layer on the low-temperature part of the inner wall of the reservoir 1. Therefore, this amount of ionized substance 4 can be released from the pores 3, thereby reducing the usable time of the ion source. Also, it is difficult to produce a stable ion beam.

The present invention has been made in view of the above, and includes a reservoir that has a pore at its tip, into which a substance to be ionized is placed, and a portion other than the pore that can be sealed; It is characterized by a heating means for maintaining the temperature, an extraction electrode disposed opposite to the tip of the reservoir, and an electron beam bombarding the tip of the reservoir.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 2 is a schematic cross-sectional view of an ion source that is an embodiment of the present invention. In the figure, the same parts as in FIG. 1 are given the same reference numerals, and the explanation thereof will be omitted. In the figure, the beam 12 1f is, for example, a heater that is uniformly wound around the bar 1. The heater 12 is heated by a heater power source 13, and is formed so that the temperature of the reservoir 1 is substantially uniform. There is. 1F-
The temperature of the bar 1 is measured, for example, by a thermocouple 14 and a voltage side 15, and its output is fed back to the heater power source 13 to maintain a preset constant temperature. 16 is a stopper for sealing the reservoir 1 and preventing vaporized vapor inside from escaping to the outside.

In the embodiment configured as described above, first, the heater 12 is heated by the heater power source 13 to heat the reservoir 1. The temperature of the reservoir 1 is maintained at a constant C temperature by a thermocouple 14 and a voltage i115, but this set temperature varies depending on the 40 types of ionized substances used; for example, in the case of cesium iodide, it is around 630 degrees Celsius. is appropriate. If this dehydration is maintained, the ionized substance 4 inside will liquefy and some will be vaporized, but since the pores 33 at the bottom of the metering arm 1 are sealed, the inside of the chamber 1f-bar 1 will remain saturated steam at that temperature. Pressure is maintained. Although the pores 3 of the reservoir 1 are exaggeratedly drawn in the figure, they actually have a diameter Q of 1 mm or less, which is extremely large.
It's hidden. Therefore, the liquefied ionized substance 4 in the IJ'-bar 1 is not released suddenly. Also, after the IJ'-bar 1 reaches the set temperature, it is always controlled at a constant temperature. Therefore, a part of the vaporized ionized substance 4 (=I) adheres to the inner wall of the reservoir 1, and the -C is not condensed, so no crystal layer is formed.When the reservoir 1 reaches the set temperature, Acceleration voltage V1 extraction voltage V2 is applied to each electrode from acceleration power source 10 and extraction power source 11.
is applied, and further by a filament power supply (not shown),
The filament 7 is heated and the tip 2 is bombarded with electrons. At this time, 'VJ! [The majority of electrons are concentrated near the tip 2.] In this case, in the conventional device, since it was necessary to heat a wide area of the reservoir 1 by electron impact, the electron flux had to be diffused to some extent, and the electron beam current irradiated to the reservoir tip 2 was inevitably reduced. As a result, the number of ion beams m generated also decreased, but in the above-described embodiment, since the reservoir 1 is heated and covered by the heater 12, the electron beam generated from the filament 7 is concentrated only on the tip 2. It is possible,
Since the ionized substance from the pores 3 can be efficiently evaporated and ionized, an ion beam with a large current can be obtained. Furthermore, conventionally, the temperature of the reservoir has been controlled by controlling the focusing and diffusion of impact electrons.
Therefore, the extraction voltage Vz (7g or Noiramen 1 to 7
The bias voltage applied to the
Since the ion current also changes as the energy of the electron beam changes, the ion beam becomes unstable as a result. In the device of this embodiment, by separating the heating of the entire reservoir 1 and the electron impact for ionization, the temperature of the reservoir 1 can be made independent of the impact of the electron beam.]
A stable ion beam can be obtained because the

FIG. 3 shows a case in which a sword-shaped member 17 made of, for example, tungsden is inserted through the pore 3 of the device of the embodiment shown in FIG. The liquefied ionized substance 4 inside the needle-like member 17 touches the tip end 1.
8, the strong electric field at the tip 18 forms a so-called Taylor-1 cone, and the ion beam can be extracted by electric field evaporation. Similar effects can be obtained because the temperature of 1 and the focusing of electron flux can be adjusted independently.

As described above, the present invention heats the reservoir by bombarding the tip of the reservoir with electrons, thereby heating and melting the ionized substance inside the reservoir and ionizing it at the same time. By separating the electron impact for ionization and independently controlling the temperature of the reservoir and the focusing of the electron flux, it is possible to extend the usable time of the ion source and obtain a stable ion beam. .

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a schematic cross-sectional view of the configuration of a conventional ion source, FIG. 2 is a schematic cross-sectional view of the configuration of an embodiment of the present invention, and FIG. 3 is a partially enlarged view of an apparatus according to an embodiment of the present invention. It is. 1: reservoir, 2: tip, 3: pore, 4: ionized substance, 5: extraction electrode, 6: frontage, 7: filament 1-.
8: accelerating electrode, 9: aperture plate, 10: accelerating power source, 11: drawing power source, 12: heater, 13: heater power source, 1/I:
Thermocouple, 15: Voltage, 16: Frame, 17: Sword-shaped member, 1
8 Two-needle member tip.

Claims (1)

[Scope of Claims] 1. A reservoir having a pore at its tip, into which a substance to be ionized is placed, and a portion other than the pore can be sealed; heating means for maintaining the temperature;
An ion source comprising an extraction electrode disposed opposite to the tip of the reservoir, and an electron generating means for bombarding the tip of the 1f-bar with an electron beam. 2. The ion source according to claim 1, wherein a sword-shaped member is disposed passing through the pore of the reliever.