JPS5875753A - Ion pump - Google Patents

Abstract

PURPOSE:To enable enhance of the exhaustion speed of an ion pump by distributing the kinetic energy of ions, which are incident upon cathodes, within an area of a large sputtering ratio by making the ion pump to have a tetrode structure containing a control electrode, which extends across the hollow space of an anode and is located apart from the center axis of the hollow space of the anode, and controlling the electric potential of a discharge space by means of the control electrode. CONSTITUTION:A control electrode 16 supports a control electrode 15 in such a manner that the electrode 15 is insulated from an anode 1, cathodes 3, collecting electrodes 4, and a vacuum case containing an ion pump. An electron group is produced in the hollow space 2 of the anode 1 by both the magnetic field of a magnet 13, and a cross electromagnetic field developed due to the difference between the electric potentials of the anode 1 and the cathodes 3. Most of ions produced from gaseous molecules due to above electron group, bump against the cathode 3 without bumping against the electrode 15, and sputters a cathode- covering matter consisting of a getter member. When the anode 1 is earthed, the electrode 15 is given a negative electric potential, and the cathodes 3 are given a negative electric potential lower than that of the electrode 15, the electric potential of electric-discharge developed in the hollow space 2 of the anode 1 is controlled by the electrode 15. As a result, the exhaustion speed of the ion pump can be increased by increasing the amount of the getter member sputtered at the cathodes 3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an ion 4 pump, and particularly to an ion 4 pump suitable for increasing the pumping speed by providing a plurality of poles.

<Prior art> Ion 4 pumps are generally used to create an oil-free Kei vacuum using cold cathode discharge in a magnetic field, and have the characteristic that they do not require mechanical movement of high-temperature or extremely low-temperature parts. This is particularly useful in fields where vacuum quality is an issue. The initial drawbacks, such as the instability of pumping speed for rare gases such as Herikumya Alpun, were resolved with the development of the three-electrode ion pump, and four-pole ion pumps with good operability were manufactured. ing.

Figure 1 is a cross-sectional view of a conventional three-electrode ion pump.
In the figure, 1 is an anode having a hollow portion 2t which passes through it, 3 is a cathode disposed close to and apart from both opening ends of the anode 1, and has a shape that covers this opening, and 4 is located further outside of the cathode 3. A collecting electrode is arranged, 6 is a power source that applies voltage to cause discharge between the anode 1 and cathode 3, 5 is a magnetic field applied from a magnetic field generator (not shown), and 4' is a field captured on the collecting electrode 4. Gas molecules 7 are gas ions generated in the hollow part 2 of the anode 1 as a result of discharge.

In this configuration, a magnetic field 5 is applied from a magnetic field 6 generating device (not shown) substantially parallel to the axis of the hollow portion 2 of the anode 1, and at the same time, a voltage V is applied from a power source 6 between the anode 1 and the cathode 3.
a is applied. By the way, in the example shown in Figure 1, the anode 1 and the collecting electrode 4 are grounded, so the potential of the cathode 3 is -Va.
becomes. As a result, a group of high-energy, high-density electrons is formed in the hollow part 2 of the anode l by the orthogonal electromagnetic fields, and the molecules that fly into the hollow part 2 are ionized and become gaseous ions 7, which enter the surface of the cathode 3 at high speed. Then, atoms on the surface of the cathode 30, which is usually made of titanium, are sputtered. The sputtered surface material of the cathode 3 adheres to the surface of the collecting electrode 4, the adhering surface material of the cathode 3 adsorbs gas molecules, and the sputtered surface material of the cathode 3 adheres thereto. The adsorbed gas molecules are embedded on the surface of the collection electrode 4 as trapped gas molecules 4I.

The embedding of molecules in the gas phase into the solid phase as described above is the pumping action of the triode ion pump.

In order to increase this pumping speed, the amount of surface material dusted off from the cathode 3 must be increased relative to the amount of gaseous io/7 formed by discharge.

#! Figure 2 is a characteristic diagram for explaining the amount of suddering of the cathode surface material in the ion pump shown in Figure 1, and the figure (jL) shows the relationship between energy U of ions incident on the surface of the cathode 30. The figure (b) shows the Sunotatsuta ratio St, expressed as the number of atoms of the cathode material sputtered per incident ion, when the energy of the incident ion is 1 or more and u ten du
The ion energy distribution function 1 is defined as the number of ions incident on the surface of the cathode 3 per unit time is fdu.
, the same figure (C) shows the snow belt vine ratio S and the horizontal fs1 of the energy distribution function f, both of which are shown as relative values.

@2), the energy distribution function f is less than θ,
The energy distribution function f is 0 above e-Va (·: unit charge), and furthermore, the energy distribution function f is almost equal to 0 within the range of the acceleration energy a-vo due to the cathode fall VO and below the anode fall.

As is clear from Fig. 2(b), the energy distribution function f takes i[t- which is not 0 only when e-VO≦u<...va- (1) f takes a large value when the energy U exceeds e·VO and is a small value, and the energy distribution function f becomes small when the energy l is large.The number Q of sputtered cathode material per unit time is given by , this integrand f-8 is shown in Fig. 2(e).As is clear from the figure, the energy U for the snow mother vine ratio S to take a large value and the energy distribution function f are large. Since the energy U where the value is taken differs greatly, basically st4
It is not possible to increase the amount of cathode material that is ejected; that is, in conventional three-electrode ion pumps, there is a limit to the pumping speed.

<Object of the invention> Therefore, the object of the present invention is to eliminate the drawbacks of the above-mentioned prior art,
To provide an ion pump in which the amount of material collected from the cathode is increased using a control electrode, and the collected cathode material is provided on a collection electrode, thereby increasing the pumping speed. be.

More specifically, the present invention adds a control electrode that penetrates the discharge space of the well-known three-pole structure at a distance from the axis of the hollow part of the anode to create a four-pole structure. The object of the present invention is to provide an ion pump that distributes the kinetic energy of ions incident on a cathode to a region with a high sputtering ratio by controlling the potential of a discharge space using a control electrode, thereby making it possible to improve the pumping speed.

(Example of the invention) Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 3 is a longitudinal cross-sectional view of an ion pump according to an embodiment of the present invention, in which parts common to each drawing are given the same reference numerals to avoid redundant explanation. In the figure, reference numeral 8 denotes a conductor column 9 which is partially insulated on the outside, supports the anode 1 and a set of two collecting electrodes 4 together with the power supply assembly 14, and electrically grounds them.
is insulated on a part of its exterior, is fixed to a power supply terminal 11 which is a part of the power supply unit assembly 14 by a connecting fitting 10, and supports a set of two cathodes 3t together with an insulating column 12. A conductor column 13 generates a magnetic field inside the hollow part 2 of the anode 1 in the direction of its penetration; 15 is a conductor column spaced apart from the axis of the hollow part 2 of the anode 1 so as to align θ with the lines of magnetic force of the magnetic field; That is, through holes (not shown) arranged in parallel with the hollow part 2 and drilled in the two cathodes 3 are inserted without contacting the cathodes 3 (insulated and penetrating the holes). A control electrode 16, which is held under appropriate tension, supports the control electrode 15 insulated from the vacuum vessel containing the anode 11, cathode 3, collection electrode 4, and ion pump.
A support member 18 that also serves as a part of the power supply route to the power supply unit 18 forms a part of the power supply unit assembly 14 and is connected to the discharge 111J (not shown) from the support member 16 via the conductive wire 17. A power supply armature t for supplying power to the control electrode 15 is shown. By the way, two cathodes 3
A large number of first type through holes 3a are formed in each of the holes.

Further, each pair of collecting electrodes 4 is arranged parallel to and spaced apart from each pair of cathodes 3 on the opposite side of the cathode 1.

Incidentally, the discharge control electrode 15 is formed of a thin wire with a small sputtering ratio, for example, a tungsten wire with a diameter of about 25 microns. A potential is applied.

In the structure as described above, its operation will now be explained in accordance with the characteristic diagram shown in FIG. By the way, No. 4 @(a),
(b) and (e) are respectively shown in Figure 2 <h>, (b) and <
In contrast to the characteristic diagram of c>, the 38th! This is to explain the amount of stagnation of the cathode surface material in the J configuration.

Now, in the configuration shown in FIG. 3, the magnetic field of the magnet 13 and li
An electron group is formed in the hollow part 2 of positive 'lk, l by the orthogonal electromagnetic field based on the potential difference between the pole 1 and the cathode 3, but most of the ions generated from the gas molecules by this electron group are transferred to the control electrode 15. It collides with the cathode 3 without colliding with the cathode 3, and sputters the cathode surface material formed by the getter material. In this case, the snow matrix ratio S to the ion incident energy U is the fourth
As shown in the figure ((turn)), there is no difference from the conventional case. Here, the anode 1 is grounded, the control electrode 15 is given a potential -Va, and the cathode 3 is given a potential -Va that is lower than the control electrode 15. Assuming that (Va+Vg) is given, 7g
is sufficiently large, for example, 600 cm or more, the state of discharge is hardly affected by Vg, and the potential of the discharge space formed in the hollow part 2 of the anode l is
, so each point takes a value thicker than -Vi-1-Vc/ (, smaller than 0.
is the sum of the potential difference corresponding to the cathode drop voltage in FIG. 1
is sufficiently small compared to the radius of the hollow part 2, vO'
is a very small value compared to viL. As shown in FIG. 4(b), the incident energy distribution function f of ions to the cathode 8 is e.g.
a) ”・Only (3) takes a non-zero value, and Fig. 2 (
Compared to the characteristic b), the discharge state is almost the same and the ion energy distribution function f has shifted to the higher energy side. As a result, the number Q of atoms of the cathode surface material sputtered by the cathode 3 per unit time is as follows, and the integrand fS is as shown in FIG. 4(C) and as shown in FIG. 2(C). This value is larger than that in conventional triode ion pumps, which has the effect of increasing the amount of getter material sputtered and increasing the pumping speed of the ion pump. In addition, since the ion pump of the present invention uses 4 tons of collecting electrodes, the pumping speed of 1 ft is stable even for rare gases.
-It is achievable.

<Effects of the Invention> As described above, according to the present invention, only a control electrode is added to the conventional 300 million-type ion pump.

It is possible to increase the pumping speed to 11 and obtain an ion pump t- which can realize a stable co-air speed ft- even for cloth gas.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional ion pump, FIG. 2 is a characteristic diagram explaining the operation of the configuration shown in FIG. 1, FIG. 3 is a cross-sectional view of an ion pump according to an embodiment of the present invention, and FIG. FIG. 2 is a characteristic diagram illustrating the operation of the 'yjc two-diagram configuration. 1...Anode, 2...Hollow part, 3--Cathode, 4...
Collection electrode, 13--Magnet, 15--Control electrode. Applicant's representative Kiyoshi Inomata Figure 3 is (KeV) 239-

Claims (1)

[Claims] an anode having a hollow portion extending through the anode; a cathode disposed close to both open ends of the hollow portion and having a plurality of through holes; a means for generating a magnetic field in the hollow portion of the anode in the direction of penetration thereof; A means for generating a voltage between one electrode, a collecting electrode spaced apart parallel to the cathode and arranged on the opposite side of the anode, and a wire with a small lug I ratio. An ion pump characterized by comprising a control electrode that is spaced apart from the axis of the pump and extends through the ion pump along the lines of magnetic force of a magnetic field, and to which a voltage between the anode and the cathode is applied.