JPH0762989B2 - Electron beam excited ion source - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electron beam excitation ion source that generates ions by an electron beam and extracts and emits the generated ions. More specifically, the present invention relates to the effect of space charge limitation. The present invention relates to an electron beam excitation ion source capable of generating a low energy, high current ion beam which is not affected.

[Conventional technology]

The applicant previously proposed an electron beam excitation ion source capable of generating an ion beam of low energy and large current by eliminating the limitation of space charge generated near the accelerating cathode for accelerating electrons (Japanese Patent Application No. (See Sho 60-132138). In this ion source, a plasma region, an accelerating cathode, an electron beam accelerating region, an accelerating anode, an ion generating region and a target cathode are provided in this order, and a negative potential with respect to the accelerating anode is applied to the target cathode. Means and
An ion extraction electrode for attracting positive ions or negative ions generated in the ion generation region and extracting the ions is provided. When the ion source is configured in this manner, the electrons in the plasma region are extracted by the accelerating anode and plunge into the ion generation region. The injected electrons collide with the inert gas (or metal vapor) in the ion generation region to generate ions, but due to the reverse flow of the ions,
The negative potential barrier formed near the exit of the accelerating cathode is neutralized. Therefore, a high-current electron beam proportional to the plasma density flows into the ion generation region. In the ion generation region, a number of ions proportional to the current value of the inflowing electron beam are generated, and the ions in the generated plasma are attracted by the ion extraction electrode and radiated to the outside of the ion generation region.

[Problems to be solved by the invention]

Even in the ion source as described above, simplification of the device structure,
Naturally, miniaturization and cost reduction are required.

[Means for trying to solve problems]

The problem described above is that the cathode, the anode (accelerating cathode), the electron beam accelerating electrode (accelerating anode), and the ion extracting electrode are arranged in this order, and a bottleneck is provided between the cathode and the anode. The problem can be solved by using an electron beam excitation ion source in which a vacuum exhaust port is provided only on the downstream side of the ion extraction electrode.

[Work]

In the present invention, since the bottleneck is provided between the cathode and the anode, the interior of the apparatus can be evacuated from the downstream side of the ion extracting electrode to make the downstream side of the bottleneck in a high vacuum state. it can.

〔The invention's effect〕

Since it is not necessary to provide an exhaust opening between the bottleneck and the ion extracting electrode, the structure of the device is simplified, and the demands for downsizing and cost reduction are satisfied. Further, even if O ₂ is introduced between the electron beam accelerating current and the ion extracting electrode, the pressure difference due to the bottleneck makes it difficult for O ₂ to flow into the cathode side and the cathode is not damaged, so that an O ⁺ beam is generated. It also has the advantage that it can.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a preferred embodiment of the present invention.
The cathode 1, which is one of the electrodes for discharging, has a cylindrical shape made of a material such as tantalum, and a discharge gas such as argon gas flows into the apparatus through a through hole 1'of the cathode. A discharge voltage of, for example, 50 is applied between the cylindrical cathode 1 and the porous anode 2 by the discharge power source 3.
0V is applied, discharge is performed, breakdown occurs, and plasma is generated by glow discharge. The discharge voltage may thus be a low voltage. Between the cylindrical cathode 1 and the porous anode 2, there is provided a fine conductance bottleneck 4, for example, a copper plate having slit-shaped or circular through-holes. This bottleneck 4 suppresses the gas pressure in the chamber on the cathode 1 side to 0.3 to 1.0 Torr, for example 0.8 Torr, and the anode 2
The gas pressure in the side chamber is controlled to 0.01 Torr to 0.04 Torr, and it also serves as an intermediate electrode. Most of the inner surface of the hole of the bottleneck 4 on the anode side is covered with an insulator 5, for example, alumina-based ceramics, so that the cathode 1 and the anode 2 can be easily discharged. An electron beam accelerating electrode 6 and ion extracting electrodes 7 and 7 ′ are provided below the anode 2. There is a distance of 0.5 to 1.5 mm between the anode 2 and the electron beam acceleration electrode 6,
An accelerating voltage is applied by the power source 8, and during this period, electrons function as an electron beam accelerating region for extracting electrons from the plasma generated by the discharge between the cathode 1 and the anode 2 and further accelerating the electrons. Further, an ion extracting voltage is applied between the electron beam accelerating electrode 6 and the ion extracting electrodes 7, 7'by power sources 9, 9 ', respectively. Between the electron beam accelerating electrode 6 and the ion extracting electrodes 7, 7 ', the accelerated electrons collide with a neutral gas to generate ions and electrons, and the generated ions are further accelerated. Function as.

The vacuum exhaust port 10 for exhausting the gas in the apparatus is provided only on the downstream side of the ion extracting electrodes 7, 7 '. When the inside of the apparatus is decompressed through the exhaust port 10, the bottleneck 4 and each part shielded by the electrode have a desired vacuum value. Specifically, the values obtained were 0.8 Torr between the cathode 1 and the bottleneck 4, 0.1 Torr between the bottleneck 4 and the anode 2, and 0.01 Torr between the electron beam accelerating cathode 6 and the ion extracting electrode 7. there were.

The voltage value that can be applied between the anode 2 and the electron beam acceleration electrode 6 is the product (P · d) of the pressure P near the anode 2 and the distance d between the anode 2 and the electron beam acceleration electrode 6. The smaller the value is, the larger the value is. However, if the distance between the anode 2 and the electron beam accelerating electrode 6 is made sufficiently small, a high voltage can be applied between the anode 2 and the electron beam accelerating electrode 6 without exhaustion. When the distance between the electrodes is short, the openings of both electrodes must be sufficiently aligned, but such a state can be easily realized by using electrodes in which metal is vapor-deposited on both sides of the porous ceramic plate. it can. A metal ion beam can be generated by introducing vapor from a metal vapor generator between the electron beam accelerating electrode and the ion extracting electrode.

If a mesh kept at a floating potential is installed in front of the anode 2, the beam can be more stably accelerated.

Further, the discharge starting voltage can be lowered by installing a filament in addition to the usual cathode. Even if the filament is used as a cathode, a relatively long life can be expected because the gas pressure in the cathode region is high. Furthermore La B
_{If 6} is used as the cathode material, it will be possible to operate for a longer life.

It is also possible to use a rod-shaped cathode instead of the cylindrical cathode and supply the discharge gas from an inlet different from the tip of the cathode.

Furthermore, it is also possible to apply an external magnetic field to the ion generation region to generate high-density plasma in this region.

For example, the ion generation region is covered with a multi-pole magnetic field on the wall surface except for the slit for extracting ions, and the potential is kept at a floating potential.A magnetic field is applied to the ion generation region perpendicularly to the incident direction of the electron beam, and the magnetic field direction is The magnetic field is applied to the ion generation region parallel to the incident direction of the electron beam to prevent the radial diffusion of the electron beam or plasma, and the direction of the incident electron beam or this direction. It is effective to extract the ion beam in the direction perpendicular to. In any case, the wall parallel to the magnetic field is kept at a potential higher than the floating potential or the plasma potential except for the vicinity of the slit. Also, it is useful to keep the wall perpendicular to the magnetic field sufficiently negative by the plasma potential. Of course, it is also possible to combine and.

Next, an embodiment in which the ion source of the present invention is applied to an ion source for an ion implantation apparatus will be described with reference to FIG. In FIG. 2, the same components as those in FIG. 1 will be described with the same reference numerals.

Airtight container, for example, a cathode 1 at one end of a cylindrical airtight container
(For example, it also serves as a gas supply tube for glow discharge). The gas pressure in the chamber on the cathode 1 side is 0.8 Tor, for example.
An orifice, for example, a slit 4 is provided so as to maintain r, and an anode, for example, a conductive plate having a thickness of 0.2 to 0.5 mm and a large number of through holes having a diameter of about 0.5 mm are provided at a position through the slit 4 or a hole or a book. An anode 2 having a fine conductor with a finer diameter than the hole diameter already provided on the electrode is provided. This anode 2 and the slit 4
The gas pressure of the chamber constituted by and is set to 0.04 Torr, for example.
The anode 2 and the cathode 1 constitute an electron beam generation source. This electron beam generation source is characterized in that the slits 4 are set to different gas pressures. For example, a minute gap may be formed in parallel with the anode 2 of the electron beam source.
An accelerating electrode 6 for accelerating the electron beam is provided at a position of 1 mm, and the accelerating electrode 6 extracts the electron beam from the electron beam generation source, accelerates it to low energy of 50 eV to 300 eV, and makes it enter the ion chamber 11. Have.

The gas pressure in the acceleration region is, for example, 0.03 Torr.A gas for ion implantation, for example, arsenic (As) gas is supplied to the ion chamber 11 at a gas pressure of 0.01 to 0.02 Torr, and the arsenic gas atmosphere is supplied. A low energy electron beam is incident. The incident low-energy electron beam collides with arsenic gas molecules to generate a dense plasma. This is because an electron beam having a large ionization cross-section is used to generate plasma in a region where the gas pressure is small, so that a dense plasma can be generated.

Ions for the ion implantation apparatus are pulled out from the plasma thus generated.

This ion derivation portion is provided with a rectangular slit 21 and an elliptical slit 22.

The configuration of the slits 21 and 22 is the electrode configuration of the ion derivation unit used in the ion source of a well-known ion implanter, and the slit 21 is a vertically long rectangular through hole of 1.5 mm × 20 mm,
The slit 22 has an elliptical shape with a short diameter of 5 mm and a long diameter of 20 mm.

The ion beam obtained through the slits 21 and 22 is emitted into a magnetic field (not shown) for mass analysis of the ion implanter. Third
The electron beam current IA1 of the electron acceleration electrode 6 and the acceleration electrode 6 are shown in the figure.
The relationship with the accelerating voltage Vac applied to is shown.

A saturation tendency appears at an acceleration voltage of about 100V. The saturation value of the electron beam is about 18% of the discharge current Id. This corresponds to the aperture ratio of the electrodes 2 and 6. The electron beam current is approximately constant even if the gas pressure is changed. The maximum value of the electron beam acceleration voltage depends on the discharge flow and gas pressure. This value decreases with increasing gas pressure above 0.03 Torr in the electron acceleration region.

Fig. 4 shows discharge current Id and accelerating electrode current (electron beam current).
The relationship of IA1 is shown. This electron beam current IA1 increases in proportion to the discharge current. The greatest advantage of the plasma ion source is that the electron beam current and energy can be controlled independently. The characteristics of electron beam excited plasma and ion extraction are as follows.

The plasma density in the ion chamber greatly affects the potentials of the ion extraction slits 21 and 22 with respect to the potential of the electron beam acceleration electrode 6. This increases due to the plasma density when an electric field sufficient to repel the primary electron beam is applied. For example, discharge source (Id) 0.5A, acceleration electrode voltage (Va
c) Plasma parameters were measured using a Langmeyer probe under the condition of 300V. That is, when the potential of the slit 21 is equal to the potential of the anode 2, the ion saturation current is 22 mA / c.
The m ² electron density is 4 × 1.0 ¹¹ / cm ³ , and the electron temperature is 0.85 eV.

As another example, the parameters when the potential of the slit 21 is floating are that the ion saturation current is 13 mA / cm ² , the electron density is 2 × 10 ¹¹ / cm ³ , and the electron temperature is 0.62 eV.

FIG. 5 shows the result of the ion extraction experiment, and the ion beam current (I _1b ) increases according to Langmeier's law.

For ion extraction, the size of the slit 21 is 1.
A rectangular through hole with a length of 5 mm and a length of 20 mm is used.

The ion beam current density is ^2.5 mA / cm ² under the following conditions.

Conditions, discharge current: 1.5 A Electron beam accelerating voltage: 250 V Voltage of ion extraction electrode (slit 21): 18 kv Capacity of ion chamber constructed in this way is 134 c
m is ^3.

When a smaller chamber is used, the maximum plasma density and a sufficient ion beam electrode density for ion implantation can be obtained.

This ion source can be constructed compactly, and an ion beam with a long life and high current density can be obtained.

[Brief description of drawings]

FIG. 1 is a side sectional view of an embodiment of the present invention. FIG. 2 is a side sectional view of an embodiment in which the present invention is applied to an ion source for an ion implantation apparatus, and FIG. 3 shows a relationship between an electron accelerating electrode, an electron beam current, and an accelerating voltage applied to the accelerating electrode.
The relationship between the discharge current and the acceleration electrode current is shown in FIG. 4, and the result of the ion extraction experiment is shown in FIG. 1 ... Cathode, 2 ... Anode, 4 ... Bottleneck, 5 ... Insulator, 6 ... Electron beam acceleration electrode, 7, 7 '... Ion extraction electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsunobu Aoyagi, 2-1, Hirosawa, Wako-shi, Saitama, RIKEN (72) Inventor Susumu Namba 2-1-1, Hirosawa, Wako, Saitama (72) ) Inventor Naoki Takayama 1-26-2, Nishishinjuku, Shinjuku-ku, Tokyo Inside Tokyo Electron Ltd.

Claims (13)

[Claims] 1. A cathode, an anode, an electron beam accelerating electrode, and an ion extracting electrode are arranged in this order, and a bottleneck is provided between the cathode and the anode. An electron beam excited ion source characterized in that a vacuum exhaust port is provided only on the downstream side. 2. The electron beam excited ion source according to claim 1, wherein the anode is provided with a large number of through holes. 3. The electron beam excitation ion source according to claim 1, wherein the distance between the anode and the electron beam accelerating electrode is 0.
An electron beam excitation ion source characterized in that it is set to 5 mm to 1.5 mm and a large number of through holes are provided in the anode. 4. The electron beam excited ion source according to claim 1, wherein the cathode is provided with a filament for causing discharge. 5. The electron beam excited ion source according to claim 1, further comprising oxygen supply means for supplying oxygen between the electron beam acceleration electrode and the ion extraction electrode. source. 6. The electron beam excited ion source according to claim 1, further comprising a metal vapor generator for introducing metal vapor between the electron beam accelerating electrode and the ion extracting electrode. Excited ion source. 7. A cathode, an anode, an electron beam accelerating electrode and an ion extracting electrode are arranged in this order, and a bottleneck is provided between the cathode and the anode, which is more than the ion extracting electrode. In an electron beam excitation ion source provided with a vacuum exhaust port only on the downstream side, a magnetic field parallel to the incident direction of the electron beam in the ion generation region formed by the electron beam acceleration electrode and the ion extraction electrode. An electron beam excitation ion source, comprising: a magnetic field applying means for applying an ion beam; and an ion extracting means for extracting an ion beam in a direction perpendicular to the incident direction of the electron beam. 8. The electron beam excited ion source according to claim 7, wherein the anode is provided with a large number of through holes. 9. The electron beam excited ion source according to claim 7, wherein the distance between the anode and the electron beam accelerating electrode is 0.
An electron beam excitation ion source characterized in that it is set to 5 mm to 1.5 mm and a large number of through holes are provided in the anode. 10. The electron beam excited ion source according to claim 7, wherein the cathode is provided with a filament for causing discharge. 11. The electron beam excited ion source according to claim 7, wherein oxygen supply means for supplying oxygen is provided between the electron beam acceleration electrode and the ion extraction electrode. source. 12. The electron beam excited ion source according to claim 7, wherein a metal vapor generator for introducing metal vapor is provided between the electron beam accelerating electrode and the ion extracting electrode. Excited ion source. 13. The electron beam excitation ion source according to claim 7, wherein in the ion generation region, a wall parallel to the magnetic field is held at a potential higher than a plasma potential, and a wall perpendicular to the magnetic field is a plasma. An electron beam excitation ion source characterized by being held at a potential lower than the potential.