JPS5987738A - Ion generation device - Google Patents

Abstract

PURPOSE:To form an ion generaton device of good gas efficiency by providing the first cathode the and second cathode on both ends of the hollow anode besides a control electrode on one side opening end while giving the potential lower than the anode and higher than the cathode to the control electrode. CONSTITUTION:The anode 1 having a hollow part 2, a magnetic field generation device 8 and a control electrode 10 made of the tubular part 10b fixed to the plate-shaped part 10a inside of the opening end of the anode 1 coaxially with the anode 1 are prepared. Further, the first cathode 11 and the second cathode 12, which has a hole 9 for ion take-out, are arranged on both ends of the anode 1 in order to form an ion generation device using crossfied discharge by giving the higher potential than the control electrode 10 to the anode while giving the lower potential that the control electrode 10 to the first cathode 11 and the second cathode 12. Accordingly, the average value of ion kinetic energy of an output beam can be easily controlled by the control electrode 10 thus improving gas efficiency by the cold cathode.

Description

[Detailed description of the invention]

[Technical Field to Which the Invention Pertains] The present invention relates to an ion generator, and more particularly to an ion generator using low-pressure gas formation and a type of crossed field discharge of electricity. [Prior art and its problems] Recently, it has been used as an ion source in the field of nuclear fusion, surface processing of semiconductors and metals (ion implantation, ion plating, etching, etc.), surface analysis, phytochemistry, etc. The use of various types of ion generators R is increasing. Typical ion sources that generate a large amount of ions are those that generate plasma and extract the ions of its constituent particles, such as Duo Plasmatron, Duo Pigatron, and non-external magnetic field arc discharge types, which are often used. I'm here. These plasma-generated ion sources have a common drawback of poor gas efficiency. Poor gas efficiency means that a large amount of neutral gas molecules θS flow out of the ion source together with the ion beam, which can easily cause dielectric breakdown in the ion acceleration section and make high-energy acceleration difficult. The beam forms a plasma around it, and the electrons are accelerated in the ion accelerator toward the ion source in the opposite direction to the ions and collide with the electrode.The electrons, which are further accelerated toward the ion source, are The number of gas molecules flowing out from the ion tube increases by increasing the number of them, so if the electrode is heated rapidly and the ions are processed for a long time, the ion electrode will be destroyed. T was also missing. Fourth, plasma-generated ion sources have a hot cathode as a source of adult supply, and it is well known that the short lifetime of the hot cathode is a common drawback of this type of ion source. To solve these drawbacks, a PIG type ion source with a cold cathode and high gas efficiency has been proposed. For example, there is an ion generator having a configuration as shown in FIG. This conventional ion generator has a cylindrical anode (1) and a pair of cathodes (31, 31, (4), a vacuum container (5) that houses these anodes (1) and cathodes (3), (4), and an anode (1) and cathodes (ffi ( 3), a lead wire (6) that applies a predetermined potential to (4), or a lead wire (6).
, (7) and a magnetic field generator (8) that applies a magnetic field in the direction of the cylinder axis of the anode (1). The anode (1) has openings at both ends, and the cathode (3),
A gap is provided between the hollow part (2) and the hollow part (2) so that a gas can enter the hollow part (2). The cathode (3) contains ions (
It is provided on the side from which the anode (Ii) is taken out, and is disk-shaped and has a through hole (9) coaxially provided in the center thereof with the hollow part (2) of the anode (1). The cathode (4) is provided opposite to the cathode (3), but is electrically connected so that they have a common potential.The anode (1) is connected to the DC power supply (t3)
), f4) are grounded via the current measuring device ([9). The current (■k) flowing here is measured by the current measuring device (c). The magnetic field generator f(8) is connected to the vacuum vessel (
5) is surrounded by a cylindrical shape, and is configured to generate a magnetic field parallel to the cylindrical axis direction of the hollow part (2) of the anode by the force of the power source (8a). The ion generator configured in this way is a vacuum container (5)
The open side (left end in the figure) is connected to, for example, an ion etching device (not shown), and the inside of the vacuum container (5) together with the ion etching device is previously evacuated to a desired degree of vacuum by an evacuation device (not shown). When operating this ion generator, a desired gas such as A gas is supplied from the ion etching device 4 side to the inside of the vacuum container (5), and the hollow part (2
) to perform air release '6mo to generate ions. The generated ions are released from the through hole (9) of the cathode (3) to the ion etching device [11,] and are used for etching. The operating conditions of the ion generator can be selected as appropriate depending on the application, but for example, the operating gas density in the vacuum container (5) is I x 1017 m'3, and the radius of the anode hollow part is? ,5. ? m, the anode-cathode cardiac pressure is 5KV, and the magnetic station is 0.15T. Ions are ejected from the opening (9) in the direction of the arrow. In other words, this ion generator is PI
The G type generates a PIG discharge, which is a type of air discharge in a space with a neutral gas molecule density in the high vacuum region, and ions generated in the discharge space are generated when the central axis of the anode space of the cathode is aligned with the cathode surface. The ions are extracted by making use of the stiffness of collisions concentrated at the intersecting parts and by providing openings in these parts of the cathode, which has the advantage of being a cold cathode and being able to manufacture one with high gas efficiency. On the other hand, (1) J., C., Helmer and R., J.,
Jensen:B:IecLricalCharac
teristics of a penning Di
charge; 1) roe. Similar to IRJ (61) 1920 (2) W, Knauer: Mechanism
of 'the Penn111g Dischar
get LOW Pressnres;
J, Appl, Phys, 3
3 (62). As shown in Figure 093, the kinetic energy of the extracted ion beam is wide, and in order to improve beam focusing and parallelism, the configuration of the beam line was extremely difficult to improve. By providing an electrode, the cold cathode has good gas efficiency, and the width of the kinetic energy of the extracted ion beam can be reduced, and furthermore, it is possible to control only the ion source without adding an ion accelerator or the like. According to
To provide an ion generator that realizes a useful function that is not possible with conventional PIG type and plasma generation type ion sources, such as greatly and easily controlling the average value of ion kinetic energy of an output beam. a plate-shaped part provided close to one opening end of the opening and covering the peripheral part of the opening described in iIJ; a control electrode consisting of a tubular part coaxial with the control electrode; a 21% cathode disposed so as to cover the hollow part of the tubular part of the control electrode; a second cathode having a through hole coaxial with the second cathode, and each of the electrodes are placed in a vacuum, a voltage is applied between the anode and the control electrode and between the control electrode and the cathode, and A magnetic field is applied in the axial direction of the hollow part of the anode, gas is introduced into the hollow part of the anode to generate an air discharge, and ions generated by this discharge are provided in the second cathode. We have invented an ion generator configured to extract ions from a hole. Figures 2 and 3 show an embodiment of an ion generator according to the invention, with Figure 2 being a circuit diagram and Figure 3 being a vertical sectional view of the main parts. .The parts common to those shown in Fig. 1 are indicated by the same symbols, and the details are ?+
l] is omitted. Although this embodiment uses common parts of the conventional device, the present invention is not limited to this and can be freely applied without departing from the gist of the present invention. The main parts of the ion generator shown in this example are an anode (1) having a hollow part (2) passing through it, and an anode (1) having a hollow part (2) passing through it.
A magnetic field generator (8) that applies a magnetic field parallel to its axis
and a plate-shaped part (10a) 4 which is arranged at a distance from and close to one opening end of the anode (1) so as to cover the periphery of the opening of the anode (1), and which is fixed thereto. A tubular portion (
+ob)c! : a control #electrode (10), a first cathode aυ disposed so as to cover the hollow part of the tubular part (Jol) of the control electrode, and a first cathode aυ disposed so as to cover the hollow part of the control electrode, and a A second cathode (1) is disposed adjacent to the anode (1) and has a through hole (9) for extracting ions coaxially drilled with the hollow part (2) of the anode. ) and the control tffl.
(14) A power supply that gives a potential higher than the 11th position of the second cathode and the second cathode (14) It is composed of a gas source (not disclosed) that supplies the gas to become ions to the middle 2P of the positive anode. In this example, two 11 poles (Ill, (13
is grounded, the potential v3 of the anode (1) and the voltage vg of the control i-electrode (1o) about 1d can be selected as appropriate, but from the characteristics of discharge, preferably 600V<Vg<V3 500
There is a relationship between V=4500V ('). Next, the effects of the present invention will be explained by comparing 0.0, a diagram showing the characteristics of the conventional embodiment, and 1. The diagram, FIG. 5, showing the characteristics of the embodiment of the present invention.Q. Figure 4 (a), (b) and Figure 5 (a), (
b) sets the space potential ■ of the discharge part in cylindrical coordinates (r,
'2) shows this. Cathode (4) or (t
The anode side surface of υ is 220, the anode side surface of the cathode (3) or α gong is 2=, 24, and the longitudinal center plane of the anode is Z '' Z 1. Hollow part of the anode. The radius of (2) is shown as 8, the anode center position is 0, and the cathode potential is 0. Figure 4(b) and Figure 5(b) show the space potential on the plane 2-z1.First, the case of a conventional device will be explained with reference to Figure 4. When voltage 3 is applied to the anode in a state where the anode is not discharged, the space potential is approximately equal to vaK near the center of the anode hollow part.This space potential is shown by the dotted line.In the state of discharge, the anode A large number of electrons are captured in the space surrounded by the hollow part and the two cathode surfaces, and the space charge caused by the electron group forms an 'α field in the anode hollow part, and the potential of the anode hollow part becomes the same as when no discharge is occurring. The potential decreases by 2. The spatial potential distribution' in the discharge state is shown by the solid line in Fig. 4(a) and (b).V
o is the cathode fall, and its value is very small compared to va in PIG discharges commonly used as ion sources. FIG. 4(C) shows the distribution of ion kinetic energy of the ion beam taken out from the shell opening (9) of the cathode. Note that the present invention does not limit the type of ions to be extracted, and charged ions may also be extracted, but charged ions that are easy to explain will be used as an example. The horizontal axis U is kinetic energy,
The vertical axis f is a distribution function in which the number of ions extracted per unit time of ions whose kinetic energy is less than or equal to U and less than u+du is fdu. Ions are generated when neutral molecules introduced into the radiation part collide with electrons and are ionized. Neutral molecules etc.'11
Due to the large mass ratio of L atoms, the kinetic energy of the ions obtained by collision is very small. The part f('1
Since the I'J position is equal to the cathode potential and is 0, the kinetic energy of the ion is actually north, and the space potential V at the site where it is generated and the cathode are accelerated by the difference in position, and the electron's If we add 5 charges to -e, we get ev. Ions are generated at a potential greater than or equal to vo and less than va, so f is eV, )≦U≦
It is possible to take a stuttering value of 0 only within the range of e Va. FIG. 4(C) is an example of actual measurement. 1) The wide distribution of f, which is a major drawback of the I () ion source, is caused by the wide distribution of the space potential from vo to va.The functions and effects of the present invention will be explained below using Fig. 5. The device according to the present invention limits the distribution of space t1 to a narrow range and realizes a narrow distribution of f.Since the potential Vg of the U control electrode (10) is externally applied, It can be considered that the space potential vg' in the hypothetical case where there is no control electrode at the position (as shown in Fig. 4) does not match the actual space potential vg'.First, considering the case where v, >vg', the electron are collided with and absorbed by the control electrode (lO), which has a low potential energy.Since the drift velocity is very large, the density of electrons decreases rapidly, and the electric field due to the space charge decreases rapidly as well.The potential va of the anode is Since it is applied from the outside, as a result of the decrease in the electric field, the space potential approaches the anodic potential, and this change progresses until it reaches v / , -Vg.The electrons undergo drift motion and axial rotation around the center of the drift; Ok, which has a larger kinetic energy than military movement,'
=vg, the α-ton density continues to decrease・■
g'〉Vg. If the difference h'-vg between vg' and
The collision with the I electrode does not cause a decrease in the ``seedling density.'' However, the ``seedling density'' increases to approach the spatial position distribution in the absence of the control electrode, and as a result, ``2'' decreases, and vg'-
This process progresses as vg is no longer excessive. Vg'
When -Vg reaches a constant value determined by the kinetic energy of one child, etc., the radiation i[ becomes stable L, and if it is not stable, it shifts to a stable state. That is, the pole has the effect of controlling the space potential, etc., as shown in FIG. .

[is the 4th
As in the case shown in Figure (c), eV(, < u (e
Only va has a non-zero value, resulting in a curve as shown in FIG. 5 (CC). The minimum value eVo of the beam can be increased to the extent necessary and technically possible.The difference between the maximum and minimum energy values e(va-V
o) is required to be above a certain value in order to maintain emission, but
Va and V. By making K as large as possible, the number γt(V −V )V represents the relative value of the energy width. vava can be made much smaller than ]. On the other hand, in the conventional device, the power supply (14) is the first effect of this invention.
), it is possible to change the value of vo without changing the equation V, =Vo. That is, the average energy of the ions can be controlled by the voltage between the cathode and the other electrodes. This is the second effect of this invention.

[Brief explanation of the drawing]

1st jXJ is a diagram showing the formation of the conventional PIG type ion generator
FIG. 3 is a cross-sectional view showing essential parts of an embodiment of the present invention, FIG. 4 is a diagram showing the characteristics of a conventional PIG ion generator, and FIG. 5 is a diagram showing the characteristics of a conventional PIG ion generator. FIG. 3 is a diagram showing characteristics of an embodiment of the present invention. (1)...anode, (2)...hollow part, (3),
(4) Cathode, (5) Vacuum vessel, (8) Magnetic field generator, (9) Ion extraction through hole, Control electrode, (LOA) Plate-shaped part , (Job)...tubular part, aυ...first 1 pole, (121-second cathode, (!3), H...id source. Figure 1 Figure 2 Figure 4 ( α) (Mu) Figure 5 (C Noji (C) ρ PiVlu

Claims (1)

[Claims] an anode shouldering the hollow portion through which the anode passes; a plate-shaped portion disposed apart from and close to one open end of the anode so as to cover the peripheral portion of the anode; A control electrode consisting of a tubular part that is fixed to the electrode, extends into the hollow part of the anode, and is coaxial with the hollow part of the anode; a first cathode, a second cathode disposed apart from and close to the other open end of the anode and having a through hole coaxially with the hollow part of the anode; means for applying a potential to the first and second cathodes, means for applying a potential lower than the control electrode potential to the first and second cathodes, and means for applying a magnetic field substantially parallel to the axis of the hollow portion of the anode; An ion generator 0 characterized in that it comprises means for supplying a gas to become ions into the hollow part of the anode.