JPS62278736A - Electron beam excited ion source - Google Patents

Abstract

PURPOSE:To aim at simplification and miniaturization in a system structure, by installing a narrow path between a cathode and an anode, and installing an evacuation port in only the more downstream side than an ion drawing out electrode. CONSTITUTION:A narrow path 4 of minute conductance is installed between a cylindrical anode 1 and a porous anode 2. At a lower stage of this anode 2, there are provided with a electron beam accelerating electrode 6 and ion drawing out electrodes 7 and 7'. And, an evacuation port 10 exhausting gas inside the system is installed only the downstream side of these ion drawing out electrodes 7 and 7'. When the inside of the system is decompressed via the exhaust port 10, each part so far intercepted by the narrow path 4 comes to the desired vacuum value. Therefore, necessity for installing an opening for exhausting between the narrow path 4 and these drawing out electrodes 7 and 7' is no longer required, so that a system construction becomes simplified and, what is more, miniaturization and low-unit cost of production can be well promoted.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an electron beam-excited ion source that generates ions using an electron beam and extracts and emits the generated ions. relates to an electron beam-excited ion source that is not affected by space charge limitations and is capable of generating a low-energy, high-current ion beam.

[Conventional technology]

The applicant previously proposed an electron beam-excited ion source that can generate a low-energy, high-current ion beam by eliminating the limitations of space charges generated near the accelerating cathode for accelerating electrons (patent application). (See No. 132138, 1983). In this ion source, a plasma region, an acceleration cathode, an electron beam acceleration region, an acceleration anode, an ion generation region, and a target cathode are provided in this order, and a negative potential is applied to the target cathode with respect to the acceleration anode. and an ion extraction electrode that attracts positive ions or negative ions generated in the ion generation region and extracts the ions. When the ion source is configured in this manner, electrons in the plasma region are extracted by the accelerating anode and rush into the ion generation region. The incoming electrons collide with the inert gas (or metal vapor) in the ion generation region and generate ions, but the backflow of these ions neutralizes the negative potential barrier that is formed near the exit of the accelerating cathode. Ru. Therefore, a large current electron beam proportional to the plasma density flows into the ion generation region. In the ion generation region, ions are generated in a number proportional to the current value of the incoming electron beam, and the generated ions in the plasma are attracted by the ion extraction electrode and emitted outside the ion generation region.

[Problem that the invention seeks to solve]

Even in the above-mentioned ion source, it is possible to simplify the device structure,
Naturally, miniaturization and cost reduction are required.

[Means for solving the problem] The problem mentioned above is that a cathode, an anode (accelerating cathode), an electron beam acceleration electrode (accelerating anode), and an ion extraction electrode are arranged in this order, and the cathode This can be solved by using an electron beam excited ion source in which a bottleneck is provided between the ion extraction electrode and the anode, and a vacuum exhaust port is provided only downstream of the ion extraction electrode.

[For production]

In the present invention, since a bottleneck is provided between the cathode and the anode, by evacuating the inside of the device from the downstream side of the ion extraction electrode, the area downstream of the bottleneck is brought into a high vacuum state. be able to.

〔Effect of the invention〕

There is no need to provide an exhaust opening between the bottleneck and the ion extraction electrode, which simplifies the structure of the device and satisfies the demands for miniaturization and cost reduction. Even if 02 is introduced between the ion extraction electrode,
Because of the pressure difference caused by the bottleneck, it is difficult for this O2 to flow into the cathode side and the cathode is not damaged, so it also has the advantage of being able to generate an O beam.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram of a preferred embodiment of the invention. A cathode 1, which is one electrode for performing discharge, is made of a material such as tantalum and has a cylindrical shape, 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°C is applied between the cylindrical cathode 1 and the porous anode 2 by a discharge power supply 3.
0■ is applied, discharge occurs and breakdown occurs, and plasma is generated by glow discharge. This discharge voltage may be as low as this. A slit-like or circular through hole is provided between the cylindrical cathode 1 and the porous anode 2 in a micro-conductance bottleneck 4, such as a conductor 74Vi.

This bottleneck 4 maintains the gas pressure in the chamber on the cathode 1 side from 0.3 to 1.
．． 0 Torr, for example, 0.8 Torr, and the gas pressure in the chamber on the anode 2 side is Q, Q ITorr to 0.04T.
It has a size that can be held within the range of 100 to 300 mm, and also serves as an intermediate electrode. Most of the inner surface of the hole in the bottleneck 4 on the anode side is covered with an insulator 5, such as alumina ceramics, so that discharge between the cathode 1 and the anode 2 can easily occur. At the lower stage of the anode 2, an electron beam acceleration electrode 6 and an ion extraction electrode 7,7' are provided. The distance between the anode 2 and the electron beam acceleration electrode 6 is 0.5
The acceleration voltage is applied by the power source 8, and during this period, an electron beam is generated which extracts electrons from the plasma generated by the discharge between the cathode 1 and the anode 2, and further accelerates the electrons. Functions as an acceleration head. In addition, an electron beam acceleration electrode 6 and an ion extraction electrode 7
．． An ion extraction voltage is applied between electrodes 9 and 7' by electrodes 9 and 9', respectively. Between the electron beam acceleration electrode 6 and the ion extraction electrode 7.7', accelerated electrons collide with neutral gas to generate ions and electrons, and an ion generation region where the generated ions are further accelerated. functions as

A vacuum exhaust port 10 for exhausting gas within the apparatus is provided only downstream of the ion extraction electrode 7,7'.

When the pressure inside the equipment is reduced through this exhaust port 10, the bottleneck 4
, each section intercepted by the electrodes has the desired vacuum value.

The specifically obtained value is 0 between cathode 1 and bottleneck 4.
．． 8Torr, Q between bottleneck 4 and anode 2, 17o
rr, the distance between the electron beam accelerating cathode 6 and the ion extraction electrode 7 is 0. It was OITorr.

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, the larger the value, but 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 evacuation. If the distance between the electrodes is short, the apertures of both electrodes must match well, but this condition can be easily achieved by using electrodes with metal vapor-deposited on both sides of a porous ceramic plate. can. Note that a metal ion beam can be generated by introducing vapor from a metal vapor generator between the electron beam acceleration electrode and the ion extraction electrode.

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

Further, by installing a filament in addition to the usual cathode, the discharge starting voltage can be lowered. Even if a filament is used as a cathode, a relatively long life can be expected due to the high gas pressure in the cathode region. Furthermore, La
If Bg is used as a cathode material, longer life operation is possible.

It is also possible to use a rod-shaped cathode instead of the cylindrical cathode, and to 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 a more dense plasma in this region.

For example, ■ Covering the wall surface of the ion generation region except for the ion extraction slit part with a multipolar magnetic field and further maintaining the potential at a floating potential; ■ Applying a magnetic field to the ion generation region perpendicular to the incident direction of the electron beam; Extracting ions in a direction perpendicular or parallel to the direction of the magnetic field, ■ Applying a magnetic field parallel to the incident direction of the electron beam to the ion generation region, preventing radial diffusion of the electron beam or plasma, and Effective methods include extracting the ion beam in this direction or in a direction perpendicular to this direction. In both cases, except near the slit, the wall parallel to the magnetic field is kept at a floating potential or a potential higher than the plasma potential. It is also necessary to keep the wall perpendicular to the magnetic field sufficiently negative by the plasma potential. Of course, it is also possible to combine ■ and ■, or ■ and ■.

Next, an embodiment in which the ion source of the present invention is applied to an ion source for an ion implantation device will be described with reference to FIG. In FIG. 2, components Be similar to those in FIG. 1 are given the same numbers and will be explained.

A cathode 1 (
For example, a pipe (also used as a supply pipe for glow discharge gas) is provided. For example, set the gas pressure in the chamber on the cathode 1 side to 0.8T.
An orifice, e.g., a slit 4, is provided so as to maintain the anode at a position through the slit 4, and an anode, e.g., a conductive plate having a thickness of 0.2 to 0.5 mm and a diameter Q of 5 m.
The anode 2 is provided with a porous conductor having a large number of through-holes of about m diameter or a conductor having a finer diameter than the holes already provided on the main electrode. This anode 2
The gas pressure in the chamber constituted by the slit 4 and the slit 4 is, for example, 0.
Set to 04 Torr. This anode 2 and cathode 1
This constitutes an electron beam source. This electron beam source is characterized in that gas pressures are set at different levels by the slits 4. Anode 2 of this electron beam source
An accelerating electrode 6 for accelerating the electron beam is provided in parallel with a micro gap, for example, 1 mm, and this accelerating electrode 6 extracts the electron beam from the electron beam generation source and accelerates it to a low energy of 5 QeV to 300 eV. It has the effect of making the ions enter the ion chamber 11.

The gas pressure in the acceleration region is, for example, 0.03 Torr, and the ion chamber 11 is filled with a gas for ion implantation, such as arsenic (As) gas, at a gas pressure of 0.01 to 0.0.
A low energy electron beam is supplied to the arsenic gas atmosphere set at 2 Torr.

This incident low-energy electron beam collides with arsenic gas molecules and generates a dense plasma. This uses an electron beam with a large ionization cross section to generate plasma in a region with low gas pressure, making it possible to generate dense plasma.

Ions for the ion implantation device are extracted from the plasma thus generated.

This ion extraction section 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 extraction section used in the ion source of a well-known ion implantation device. 5vn major axis 2Q+n
It has an elliptical shape of m.

The ion beam that has passed through the slits 21 and 22 is emitted into a magnetic field (not shown) for mass analysis of the ion implanter.

FIG. 3 shows the relationship between the electron beam current IAI of the electron accelerating electrode 6 and the accelerating voltage Vac applied to the accelerating electrode 6.

A tendency to saturation appears at an acceleration voltage of about 100 μ.

The saturation value of the electron beam is about 18% of the discharge current 1d. This corresponds to the aperture ratio of the electrode 2.6.

The electron beam current remains approximately constant even if the gas pressure is changed. The maximum value of the electron beam acceleration voltage depends on the discharge current and gas pressure. This value decreases as the gas pressure increases above 0.03 Torr in the electron acceleration region.

Figure 4 shows the discharge current 1d and the accelerating electric current l! ! ! The relationship between current (electron beam current) IAI is shown. This electron beam current IA
I increases in proportion to the discharge current. The biggest advantage of a plasma ion source is that the current and energy of the electron beam 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 influences the potential of the ion extraction slit 21,22 relative to the potential of the electron beam accelerating electrode 6. This becomes higher due to the plasma density when a sufficient electric field is applied to repel the primary electron beam. For example, the discharge source (I d ) 0.5 A
, plasma parameters were measured using a Langmeyer probe under the conditions of accelerating electrode voltage (Vac) of 300 μ.

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++l, and the electron density is 4.
×108/cIll, the electron temperature is 0.85 eV.

As another example, each parameter when the potential of the slit 21 is floating is such that the ion saturation current is 13 mA/cm.
, electron density 2X10H/cut, electron temperature 0.62e
It is V.

FIG. 5 shows the results of an ion extraction experiment, where the ion beam current (fib) increases according to Langmeyer-Child's law.

For ion extraction, the slit 21 uses a rectangular through hole having a width of 1.5 mm and a length of 2 Q mm as described above.

The ion beam current density is 2.5 mA under the following conditions.
/cffl.

Conditions, discharge current: L 5 A Electron beam acceleration voltage: 250V Voltage of ion extraction electrode (slit 21): gkv The capacity of the ion chamber configured in this way is 13
4 cnl.

The highest plasma density and sufficient ion beam electrode density for ion implantation can be obtained when a smaller chamber is used.

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

[Brief explanation of drawings]

FIG. 1 is a side sectional view of one embodiment of the present invention. FIG. 2 is a side cross-sectional view of an embodiment in which the present invention is applied to an ion source for an ion implantation device, and FIG.
The relationship between the discharge current and the accelerating electrode current is shown in FIG. 4, and the results of the ion extraction experiment are shown in FIG. 5, respectively. 1... cathode, 2... anode, 4... bottleneck, 5... insulator,
6...Electron beam acceleration electrode, 7.7'...
...Ion extraction electrode. Figure 3 Vac (V) Figure 4 Id (A) Vex (kV) Procedure amendment writing method) Commissioner of the Patent Office Kuro 1) Akio Tonoen 1, Indication of the case Patent Application No. 121967 of 1985 2, Invention Name: Electron Beam Excited Ion Source 3, Relationship to the Amendment Person Case: Applicant Name (679) RIKEN Tokyo Electron Co., Ltd. 4, Agent

Claims (1)

[Claims] A cathode, an anode, an electron beam acceleration electrode, and an ion extraction electrode are arranged in this order, a bottleneck is provided between the cathode and the anode, and a vacuum exhaust port is provided only downstream of the ion extraction electrode. An electron beam-excited ion source equipped with