JP3379151B2 - Microwave ion source - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave type ion source which is used in, for example, an ion implantation apparatus and produces a plasma by a microwave discharge in a magnetic field to extract ions from the plasma.

[0002]

2. Description of the Related Art In recent years, ion sources for converting elements into plasma and extracting ions in the plasma as ion beams have been used in various fields including an ion implantation apparatus. This ion source includes a microwave type ion source that generates plasma by microwave discharge in a magnetic field.

As shown in FIG. 5, this microwave type ion source has a plasma chamber 54 to which a waveguide 56 for transmitting microwave power output from a magnetron is connected. In addition, the plasma chamber 5
A vaporizer for evaporating the solid ion source substance and introducing it into the chamber, a gas introducing pipe for introducing a carrier gas such as a gas ion source substance and argon gas into the chamber 4 are also connected to 4. .

The wall surface of the plasma chamber 54 on the side of the waveguide 56 is made of a high dielectric material such as boron nitride (BN) for introducing the microwave power transmitted by the waveguide 56 into the chamber. A microwave introduction window 55 is provided.

A source magnet 59 is provided around the plasma chamber 54 to form a magnetic field substantially parallel to the beam extraction direction inside the chamber.

In this ion source, the microwave power output from the magnetron is transmitted through the waveguide 56 and the microwave introduction window 55 to the plasma chamber 5.
In the magnetic field formed by the source magnet 59, the ion species introduced into the chamber are turned into plasma by microwave discharge.

A plasma slit 51 having, for example, a slit-shaped ion outlet 51a is formed on the wall surface of the plasma chamber 54 facing the microwave introduction window 55, and outside the plasma chamber 54. An extraction electrode 57 is provided so as to face the plasma slit 51.

The ion source is the plasma chamber 5
4 and the extraction electrode 57, the plasma chamber 54 generates a positive potential difference from the extraction electrode 57 to apply a strong external electric field, and by this external electric field, ions are extracted from the ion extraction port 51a of the plasma slit 51. ,
It is designed to form an ion beam.

By the way, when plasma is generated in the plasma chamber 54, the inner wall of the chamber is sputtered by the plasma forming substance, and the resulting substance adheres to the microwave introduction window 55 and the inner wall of the chamber. If a conductive substance adheres to the microwave introduction window 55, the microwave is absorbed by the conductive substance,
Since there is a problem in that the efficiency of incidence of microwaves on the inside of the plasma chamber 54 decreases, the inside of the plasma chamber 54 is usually made of boron nitride (B) so that the substance generated by the sputtering becomes an insulator.
It is covered with a shield member 52 made of an insulating material such as N).

[0010]

Even if the inner surface of the plasma chamber 54 is covered with an insulating material as described above, it is difficult to prevent the conductive material from completely adhering to the microwave introduction window 55. Yes, with the operating time of the ion source,
The conductive material adhering to the microwave introduction window 55 gradually increases, and the microwave plasma chamber 54
It is unavoidable that the efficiency of incidence on the inside will drop.

This is because the substance serving as an ionic species is conductive, or the binder substance contained in the shield member 52 and used at the time of producing the material (BN) is
This is because the plasma-forming substance may cause sputtering to generate a conductive substance.

As described above, when the conductive material adheres to the microwave introduction window 55 to reduce the incidence efficiency of microwaves into the plasma chamber 54, the plasma generated in the plasma chamber 54 becomes inadequate. Becomes stable,
Therefore, the beam current drawn from the plasma chamber 54 decreases and becomes unstable. And finally, it becomes impossible to generate plasma.

In the conventional ion source, the use time is restricted by the above phenomenon and the life is short.

The present invention has been made in view of the above, and an object thereof is to provide a microwave type ion source capable of extending the life and obtaining a stable ion beam for a long time.

[0015]

The microwave type ion source of the present invention comprises a waveguide means for propagating a microwave and a dielectric for guiding the microwave propagated by the waveguide into the chamber. A plasma chamber having a microwave introduction window is provided, and in order to solve the above problems, the following measures are taken.

That is, a cone-shaped protrusion having an inclination with respect to the microwave propagation direction is formed on the surface of the inside of the chamber in the microwave introduction window.

Further, a plurality of protrusions are formed.
Preferably.

[0018]

According to the above structure, since the projection portion is formed on the chamber inner surface side of the microwave introduction window portion, the surface area of the microwave introduction window portion on the chamber inner surface side is smaller than that of the conventional flat type. Is getting bigger. For this reason, the deposition rate of the conductive substance per unit area in the microwave introduction window portion is lower than in the conventional case.

By increasing the area of the surface portion of the microwave introduction window portion on the inner side of the chamber, it is possible to suppress the decrease of the extraction beam current caused by the adhesion of the conductive material to the microwave introduction window portion, and to stabilize the extraction beam current. Of the ion source, and the life of the ion source can be extended.

Further, by forming a plurality of protrusions,
The area of the surface of the microwave introduction window inside the chamber
To further expand the life of the ion source and increase its effect.
You can

[0021]

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

The microwave type ion source of this embodiment is an electron cyclotron resonance (ECR).
An ECR ion source that generates a plasma by generating a microwave discharge in a magnetic field under the onance condition and extracts ions from the plasma as a beam, and is mounted on, for example, an ion implantation apparatus.

The ion source has, for example, a magnetron (not shown) that outputs a microwave of 2.45 GHz and a magnetron power supply (not shown) that operates the magnetron. As shown in FIG. 1, it is connected to the plasma chamber 4 via a waveguide 6 as a wave guide means for propagating microwaves.

A microwave introducing window 5 for introducing microwave power into the chamber is provided on the wall surface of the plasma chamber 4 on the side of the waveguide 6. The microwave introduction window portion 5 is made of a high melting point material, such as BN, which has a relatively high permittivity through which microwaves can pass, and has high corrosion resistance and high temperature resistance. There is.

The microwave introduction window portion 5 of this embodiment is not a flat surface portion as in the conventional case, but a cone-shaped protrusion having an inclined surface with respect to the microwave propagation direction on the inside surface of the chamber. The part 5a is formed.

In the plasma chamber 4, a vaporizer (not shown) for evaporating the solid ion source material and introducing it into the chamber, and a gas ion source material such as BF3 and a carrier gas such as Ar are stored in the chamber. A gas introduction pipe (not shown) for introducing the gas into the inside is connected to each.

The outer wall of the plasma chamber 4 is made of metal such as stainless steel, while the entire inner surface is covered with a shield member 3 made of an insulating material such as BN.

A plasma slit 1 having a slit-shaped ion outlet 1a is formed on the wall surface of the plasma chamber 4 facing the microwave introduction window 5.

In the ion extraction direction from the plasma slit 1, an extraction electrode 7 having a beam passage hole 7a and a deceleration electrode 8 having a beam passage hole 8a are arranged in this order.

The deceleration electrode 8 is grounded to the ground potential,
A negative voltage Vd is applied from the deceleration power supply 13 so that the extraction electrode 7 has a negative potential than the deceleration electrode 8 . Then, the plasma chamber 4 has a drawing power source 1
4 is connected to a positive electrode terminal, and a high-voltage extraction voltage Ve is applied from the extraction power source 14.
Accordingly, the plasma chamber 4 (the plasma chamber 4
Potential difference (Ve + Vd) is generated between the plasma slit 1) of the plasma slit 1) and the extraction electrode 7, and a strong external electric field is formed. This external electric field causes positive ions in the plasma generated in the plasma chamber 4 The ion beam is extracted from the first ion extraction port 1a to form an ion beam. As described above, by setting the extraction electrode 7 to a negative potential than the deceleration electrode 8, it is possible to prevent the backflow of electrons (a phenomenon in which electrons flow into the plasma chamber 4) generated downstream of the extraction electrode 7. It has become.

The extraction electrode 7 and the deceleration electrode 8 are provided together with the plasma chamber 4 in a vacuum chamber (not shown) in a high vacuum state.

A source magnet 9 having a solenoid coil is arranged around the plasma chamber 4, and the source magnet 9 generates a magnetic field in the plasma chamber 4 which is substantially parallel to the beam extraction direction. To form. The solenoid coil has
A source magnet power supply (not shown) is connected, and a source magnet current is supplied from the source magnet power supply.

The operation of the ion source in the above structure will be described.

First, an ion source material is introduced into the plasma chamber 4, and a source magnet current is supplied to the solenoid coil of the source magnet 9 from a source magnet power source, so that a magnetic field substantially parallel to the beam extraction direction is introduced into the plasma chamber 4. Is formed. In addition, the magnetron is activated, and the output of microwave power is started.

The microwave power is applied to the waveguide 6
Is transmitted by the plasma chamber 4, reaches the microwave introduction window 5, passes through the microwave introduction window 5, and passes through the plasma chamber 4
Will be introduced in. Then, the ion source material introduced into the plasma chamber 4 is turned into plasma by the microwave discharge due to the ECR phenomenon.

A potential difference (Ve + Vd) is generated between the plasma slit 1 of the plasma chamber 4 and the extraction electrode 7, and a strong external electric field formed by this potential difference causes a positive electric field in the plasma in the plasma chamber 4. Ions are extracted and an ion beam is formed.

When the plasma is generated in the plasma chamber 4, the shield member 3 is sputtered by the plasma forming substance, so that the conductive substance such as the binder substance contained in the shield member 3 is converted into the plasma chamber. 4 is generated in the microwave introduction window 5
As described in the prior art, it may be attached to the. Also, when a conductive ionic species is used, the conductive substance adheres to the microwave introduction window portion 5.

However, since the projection portion 5a is formed on the chamber inner surface side of the microwave introduction window portion 5 of this embodiment, the surface area on the chamber inner surface side is larger than that of the conventional flat type. Therefore, in this embodiment, the deposition rate of the conductive substance per unit area in the microwave introduction window portion 5 is lower than that in the conventional case.

As the inclination angle of the cone-shaped protrusion 5a with respect to the microwave propagation direction becomes more acute, the surface becomes
Although the area of the part becomes large , the amount of reflected microwaves also increases and the utilization efficiency of microwaves decreases, so
It is desirable to experimentally set the tilt angle to the optimum angle.

As described above, the ECR ion source of this embodiment has the waveguide 6 for propagating the microwave and the dielectric microwave for guiding the microwave propagated by the waveguide 6 into the chamber. A plasma chamber 4 having an introduction window portion 5 is provided, and the inside of the chamber in the microwave introduction window portion 5 is
Since the cone-shaped protrusion 5a having an inclination with respect to the microwave propagation direction is formed on the surface portion,
The increase of the area of the surface of the microwave introduction window 5 on the inner side of the chamber and the heat generation can suppress the decrease in the extraction beam current caused by the adherence of the conductive material to the microwave introduction window 5, thus stabilizing the extraction beam current. Of the ion source, and the life of the ion source can be extended.

Although only one cone-shaped protrusion 5a is formed in the central portion of the microwave introduction window 5 in the above description, the invention is not limited to this. Modifications of the microwave introduction window 5 are shown in FIGS. As shown in FIG. 2 and FIG. 3, the protruding portion 5 is formed in the microwave introduction window portion 5.
Two or more a's may be formed. The more the formation of the projecting portion 5a is increased, the area of the surface portion is increased,
The effect of extending the life of the ion source is also increased.

The above-mentioned embodiments are merely for clarifying the technical contents of the present invention, and should not be construed in a narrow sense by limiting only to such specific examples. Various modifications can be made within the scope of the claims.

[0043]

As described above, the microwave ion source of the present invention has a dielectric for guiding the microwave propagating into the chamber and the microwave propagated by the waveguide. And a plasma chamber having a microwave introduction window part, wherein a cone-shaped projection having a surface portion inclined with respect to a microwave propagation direction is provided inside the chamber in the microwave introduction window part. This is a structure in which a part is formed.

Therefore, the surface area of the microwave introduction window portion on the inner surface side of the chamber is larger than that of the conventional flat type. Therefore, the deposition rate of conductive material per unit area in the microwave introducing window portion lower than conventional. Therefore, in this microwave type ion source,
It is possible to suppress the decrease in the extraction beam current caused by the adhesion of the conductive material to the microwave introduction window, to improve the stability of the extraction beam current, and to achieve the effect of extending the life of the ion source. Play.

Further , the microwave type ion source of the present invention is
In the microwave type ion source with the above configuration,
It is a structure in which a number of units are formed.

Therefore, the chamber of the microwave introduction window
The surface area on the inner surface side is further expanded to increase the life of the ion source.
This has the effect of making the fruit larger.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is a schematic cross-sectional view of a microwave type ion source (ECR ion source).

FIG. 2 is a cross-sectional view showing a modified example of a microwave introduction window portion of the ion source.

FIG. 3 is a cross-sectional view showing another modification of the microwave introduction window portion of the ion source.

FIG. 4 is a cross-sectional view showing still another modified example of the microwave introduction window portion of the ion source.

FIG. 5 shows a conventional example and is a schematic cross-sectional view of a microwave ion source (ECR ion source).

[Explanation of symbols]

1 plasma slit 1a Ion outlet 3 Shield member 4 Plasma chamber 5 Microwave introduction window 5a protrusion 6 Waveguide 7 Extraction electrode 8 Deceleration electrode 13 Deceleration power supply 14 Drawout power source

Claims (2)

(57) [Claims] 1. A plasma chamber having a waveguide for propagating microwaves and a dielectric microwave introduction window for guiding the microwaves propagated by the waveguide into the chamber. In the microwave ion source, on the inside of the chamber in the microwave introduction window,
On the surface, a coil having an inclination with respect to the microwave propagation direction
A microwave-type ion source, characterized in that a horn- shaped protrusion is formed. 2. A plurality of protrusions are formed.
The microwave type ion source according to claim 1, which is a characteristic.