JPH07169425A - Ion source - Google Patents

Abstract

PURPOSE:To prolong the life of a cathode and enhance the yield of a polyvalent ion. CONSTITUTION:Ionization is performed in a second electric discharge chamber 5 by utilizing an electron of a plasma produced in a first electric discharge chamber 4 by arc discharge. The plasma electron produced in the first electric discharge chamber 4 is flown between an intermediate electrode 6 and a reflection electrode 14 in a reciprocating manner while being turned by the effect of a magnetic field of a solenoid 2 and an electric field of an anode 10, to be thus confined. Consequently, it is possible to enhance ionization efficiency so as to improve a yield of an ion. Additionally, sine a nozzle port 6a and the reflection electrode 14 are disposed near, an extraction slit 11 with respect to the center of an arc chamber 1, a plasma axis approaches the extraction slit 11 so that a polyvalent ion distributed much in the middle portion between the nozzle port 6a and the reflection electrode 14 is extraction through the extraction slit 11. Furthermore, an arc voltage in the first electric discharge chamber 4 is restrained to a lower level, thereby reducing energy generated when a filament 7 is sputtered by the electron.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion source which is used in an ion implantation apparatus or the like and is capable of producing more multiply-charged ions.

[0002]

2. Description of the Related Art As an ion source serving as an ion beam generation source, there is a so-called electron oscillation type ion source in which electrons involved in ionization are vibrated between two electrodes. There are various types of electronic vibration type ion sources, but PI is a typical example.
G (Penning Ionization Gaug)
e) type ion source. This ion source is configured to confine the electrons emitted from the filament by a magnetic field and a reflective electrode and use them for ionization. PIG
The ion type ion source strongly confine electrons as described above, so that it is possible to generate multiply charged ions having a valence of 2 or more.

Generally, the following two cases can be considered for the production of multiply charged ions. The first is the case where a relatively high energy electron collides with a gas molecule and a few electrons are removed from the gas molecule at a time. The second is a case where monovalent ions generated by collision with electrons further collide with electrons and the electrons are removed. The amount of multiply-charged ions generated in the second case is proportional to the product of the ion confinement time and the ionization electron density. Therefore, in order to increase the production amount of multiply-charged ions, the confinement of ions should be strengthened and the confinement time of ions should be lengthened. Further, the probability of collision of monovalent ions with ionized electrons (collision cross-sectional area) depends on the energy of the electrons, and therefore it is necessary to increase the discharge voltage.

In order to generate a multiply charged ion source with a PIG type ion source, the discharge voltage is increased as described above (several hundreds of volts).
Need). However, when the discharge voltage is increased, the energy for the positive ions generated in the ion source to sputter the filament is also increased, so that the consumption of the filament is accelerated and the life of the filament is generally short. Duoplasmatron and Duopigatron are examples of ion sources that have solved such problems.

The Duoplasmatron is designed to compress cathode plasma emitted from a filament by means of a nozzle-shaped intermediate electrode to generate high-density plasma and extract ions from the axial direction of the plasma. In this duoplasmatron, since the filament is present on the side of the cathode plasma having a relatively low density, it is less susceptible to sputtering.

The duopigatron is a mixed type of a PIG type ion source and a duoplasmatron, and has both advantages.

[0007]

However, since the duoplasmatron and duopigatron are configured to extract ions in the axial direction of the plasma, it is impossible to efficiently collect multiply charged ions. Have a point. In particular, the PIG type ion source is not suitable for extracting polyvalent ions in a high yield because a large amount of polyvalent ions are distributed in the intermediate portion between the cathode and the reflective electrode, as described below.

Generally, the amount of multiply-charged ions produced is proportional to the product of ion confinement time and ionization electron density.
In the structure that causes G discharge, the ion confinement time becomes longer in the central part of the anode than in the vicinity of the cathode. In addition, the generated ions are accelerated toward the cathode and the reflective electrode due to the potential difference between the cathode and the anode, but in the middle of them, charge conversion due to collision with particles and recombination with electrons in plasma are performed. , Some are converted to low valence ions.

For the above reasons, many multiply-charged ions are present in the intermediate portion between the cathode and the reflective electrode. Due to the same reason, in duopigatron, many multiply-charged ions are present in the intermediate portion between the intermediate electrode and the reflective electrode.

Therefore, in the structure in which the ions are extracted from the axial direction like the PIG ion source, the ions are extracted from the site where the distribution of the multiply-charged ions is small, and the yield of the multiply-charged ions is not so high.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an ion source capable of obtaining multiply-charged ions in a high yield.

[0012]

In order to solve the above-mentioned problems, the ion source of the present invention includes a first discharge chamber and a second discharge chamber that generate a gas discharge to generate plasma. A filament (cathode) provided to emit electrons
An intermediate electrode that is provided between the first discharge chamber and the second discharge chamber and has a nozzle-shaped opening that connects the discharge chambers to each other, and that is kept at a higher potential than the filament; An anode provided in the second discharge chamber and kept at a higher potential than the filament and the intermediate electrode, and an anode provided in the second discharge chamber so as to face the opening of the intermediate electrode and kept at the same potential as the intermediate electrode. A reflecting electrode and a magnetic field generator for applying a magnetic field to the first and second discharge chambers along the axial direction of the plasma, and the second discharge chamber is substantially intermediate between the intermediate electrode and the reflective electrode. It is characterized in that it has an extraction port for extracting ions in a direction orthogonal to the axial direction of the plasma at the site, while the opening of the intermediate electrode and the reflection electrode are arranged near the extraction port.

[0013]

In the above structure, gas discharge (arc discharge) occurs due to the potential difference between the filament and the intermediate electrode, and the gas in the first discharge chamber changes to the plasma state. The electrons in the plasma are focused by the nozzle-shaped opening of the intermediate electrode and
Guided to the discharge chamber. In the second discharge chamber, plasma electrons
Energy is provided by the potential difference between the intermediate electrode and the anode and used for ionization.

At this time, since the opening of the intermediate electrode and the reflective electrode are provided so as to face each other, plasma electrons reciprocate between the intermediate electrode and the reflective electrode due to the potential difference between the intermediate electrode and the reflective electrode and the anode. While moving, it makes a swirling motion due to the magnetic field provided by the magnetic field generator. Therefore, the effective flight distance of plasma electrons in the second discharge chamber becomes long, ionization is promoted, and multiply charged ions are easily generated.

The polyvalent ions generated by this ionization are distributed in a large amount at almost the intermediate portion between the intermediate electrode and the reflective electrode as described above. Therefore, by arranging the opening of the intermediate electrode and the reflective electrode near the outlet of the second discharge chamber, the multiply-charged ions can be easily extracted from the outlet.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS. 1 and 2.

As shown in FIG. 1, the ion source according to this embodiment comprises an arc chamber 1, a solenoid 2 and an extraction electrode system 3.

The solenoid 2 is adapted to generate a magnetic field so as to apply a magnetic field in the direction of arrow B in the drawing to the arc chamber 1. Further, the extraction electrode system 3 is arranged in a direction substantially orthogonal to the direction of the above-mentioned magnetic field with respect to an extraction slit 11 described later provided in the arc chamber 2, and an ion beam is drawn from the extraction slit 11 by an arrow I in the figure. It is designed to be pulled out in the direction.

The arc chamber 1 includes a first discharge chamber 4 and a second discharge chamber 4.
And a discharge chamber 5. First discharge chamber 4 and second discharge chamber 5
Are separated from each other by an intermediate electrode 6 having a nozzle opening 6a. The nozzle opening 6a as an opening is formed in a nozzle shape so as to protrude toward the second discharge chamber 5 side.

A filament 7 is provided in the first discharge chamber 4. The filament 7 as a cathode is drawn into the first discharge chamber 4 by bushings 8 attached to penetrate both side walls of the arc chamber 1, and is wound in a single coil. Further, a gas introduction port 9 for introducing gas is provided through the side wall of the first discharge chamber 4.

The second discharge chamber 5 is composed of an anode (anode) 10 having a bottomed cylindrical shape, and the anode 10 is provided with a drawing slit 11 as a drawing port. The extraction slit 11 is an opening for extracting the ion beam, and as shown in FIG. 2, is formed in a rectangular shape and spreads from the inside to the outside.

An insulating member 12 is interposed between the anode 10 and the intermediate electrode 6. Further, in the second discharge chamber 5, at a position facing the intermediate electrode 6 of the anode 10,
The reflective electrode 14 is attached by an attachment member 13 made of an insulating material. The reflective electrode 14 has a flat surface that faces the intermediate electrode 6.

In the above-mentioned arc chamber 1, the coil portion of the filament 7, the nozzle port 6a of the intermediate electrode 6 and the reflecting electrode 14 are aligned on a straight line parallel to the direction of the magnetic field and are drawn out to the center of the arc chamber 1. It is arranged near the slit 11. With such an electrode arrangement, the axis of the plasma generated in the arc chamber 1 coincides with the direction of the magnetic field and becomes close to the extraction slit 11.

Both ends of the filament 7 are connected to a filament power source 15, and power is supplied from this filament power source. Further, between the one end of the filament 7 to which the positive electrode of the filament power supply 15 is connected and the intermediate electrode 6 and the reflection electrode 14,
The arc power supply 16 is connected. Further, the intermediate electrode 6
A second arc power supply 17 is connected between the anode 10 and the anode 10. As a result, the intermediate electrode 6 and the reflective electrode 14 are set to have the same potential, and both electrodes 6 and 14 are set to have a higher potential than the filament 7 and a lower potential than the anode 10.

In the ion source configured as described above, gas is introduced into the arc chamber 1 through the gas inlet 9 to fill the first discharge chamber 4 with gas. Further, the first arc power source 1 is provided between the filament 7 and the intermediate electrode 6.
6, a voltage of 50 V to 100 V is applied as the primary discharge voltage.

In this state, the filament 7 generates heat by being supplied with power from the filament power source 15 and emits thermoelectrons to the first discharge chamber 4. This makes the first
Arc discharge occurs in the discharge chamber 4, and the gas particles of the gas collide with the thermoelectrons to form plasma composed of impurity ions and electrons. And the electrons in this plasma are
The nozzle port 6a of the intermediate electrode 6 is attracted to the intermediate electrode 6.
And is guided to the second discharge chamber 5.

In the second discharge chamber 5, a voltage of 100V to several hundreds of V is applied as a secondary discharge voltage by the second arc power supply 17 between the intermediate electrode 6 and the anode 10. In this state, ionization is promoted by plasma electrons from the first discharge chamber 4, and plasma is generated. At this time, the plasma electrons are swung between the intermediate electrode 6 and the reflective electrode 14 while swirling under the action of the magnetic field generated by the solenoid 2 applied in the plasma axis direction and the electric field generated by the anode 10 orthogonal to the magnetic field. Fly back and forth.

As described above, by confining the plasma electrons obtained in the first discharge chamber 4 by the magnetic field and the electric field, the ionization efficiency is increased and more multiply charged ions are generated. Further, since the arc chamber 1 has a structure in which the plasma axis is located near the extraction slit 11,
It is possible to extract more multiply-charged ions, which are mostly distributed in a substantially intermediate portion between the intermediate electrode 6 and the reflective electrode 14.

Further, the second discharge chamber 5 is discharged by a high arc voltage, while the first discharge chamber 4 is discharged by a low arc voltage, so that the energy of the filament 7 sputtered by electrons can be suppressed low. It is possible to reduce the consumption of the filament 7. Therefore, the life of the filament 7 can be extended as compared with a PIG type ion source having a single discharge chamber.

[0030]

INDUSTRIAL APPLICABILITY As described above, the ion source of the present invention produces the plasma by generating the gas discharge.
A discharge chamber, a cathode that is provided in the first discharge chamber and emits electrons, and a nozzle-shaped opening that is provided between the first discharge chamber and the second discharge chamber and connects the discharge chambers to each other. And an intermediate electrode which is kept at a higher potential than the cathode, an anode which is provided in the second discharge chamber and is kept at a higher potential than the cathode and the intermediate electrode, and the intermediate electrode in the second discharge chamber. A reflecting electrode that is provided so as to face the opening portion of the intermediate electrode and is kept at the same potential as the intermediate electrode, and a magnetic field generator that applies a magnetic field to the first and second discharge chambers in the axial direction of the plasma. While the second discharge chamber has an outlet for extracting ions in a direction orthogonal to the axial direction of plasma at a substantially intermediate portion between the intermediate electrode and the reflective electrode, the opening of the intermediate electrode and the reflective electrode have the outlet. Located near the exit It is configured to have.

As a result, the electrons in the plasma generated by the gas discharge in the first discharge chamber are used to perform ionization in the second discharge chamber. In the second discharge chamber, the plasma electrons from the first discharge chamber are confined by the electric field formed by setting the potentials of the intermediate electrode, the reflective electrode and the anode and the magnetic field by the magnetic pole. Therefore, the effective flight time of plasma electrons in the second discharge chamber becomes long, the generation of ions is promoted, and the amount of multiply-charged ions generated can be increased.

Furthermore, since the opening of the intermediate electrode and the reflecting electrode are arranged near the outlet of the second discharge chamber, the plasma axis is close to the outlet, and more multiply-charged ions can be extracted. Then, in the first discharge chamber, since it is only necessary to generate plasma electrons used to generate ions in the second discharge chamber, the discharge voltage applied between the cathode and the intermediate electrode is lowered (100 V or less). The energy with which the cathode is sputtered can be kept low.

Therefore, if the present invention is adopted, there is an effect that the life of the cathode can be extended and an ion source with an increased yield of multiply-charged ions can be provided.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a configuration of a main part of an ion source according to an embodiment of the present invention.

FIG. 2 is a front view showing a shape of an extraction slit of an arc chamber in the ion source.

[Explanation of symbols]

 2 Solenoid (magnetic field generator) 4 First discharge chamber 5 Second discharge chamber 6 Intermediate electrode 6a Nozzle mouth (opening) 7 Filament (cathode) 10 Anode (anode) 11 Drawing slit (drawing exit) 14 Reflective electrode 16 1st Arc power supply 17 Second arc power supply

Claims (1)

[Claims] 1. A first and a second discharge chamber for generating a gas discharge to generate plasma, a cathode provided in the first discharge chamber for emitting electrons, the first discharge chamber and the second discharge. An intermediate electrode that is provided between the discharge chamber and the discharge chamber, and has a nozzle-shaped opening that connects the discharge chambers to each other, and that is kept at a higher potential than the cathode; An anode kept at a higher potential than the electrode, a reflection electrode provided in the second discharge chamber so as to face the opening of the intermediate electrode and kept at the same potential as the intermediate electrode, and the first and second electrodes. A magnetic field generator for applying a magnetic field to the discharge chamber along the axial direction of the plasma, wherein the second discharge chamber is arranged at a substantially intermediate portion between the intermediate electrode and the reflective electrode in a direction orthogonal to the axial direction of the plasma. Have an outlet to pull out On the other hand, an ion source, wherein the openings and the reflection electrodes of the intermediate electrode is disposed on the outlets closer.