JPH03257748A - Ion generating method - Google Patents

Abstract

PURPOSE:To elongate the life time of a filament and to reduce the frequency of maintenance so as to improve the productivity of a device by supplying an AC current to the filament to heat it. CONSTITUTION:An AC voltage Vf is applied to a filament 4 to heat it with an AC current. A DC discharge voltage Vd is applied between the filament 4 and an electron generating chamber 2, thereby a discharge gas such as argon gas introduced in the electron generating chamber 2 from an intake 5 of the discharge gas is discharged to make plasma. Hence the consumption of the filament 4 is made more uniform than that in DC current heating of the filament 4. Thereby the life time of the filament 4 can be elongated, and the frequency of maintenance can be reduced to improve the productivity.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) TECHNICAL FIELD The present invention relates to an ion generation method.

(Prior Art) In general, an apparatus that performs processing by applying predetermined ions to a workpiece, such as an ion implantation apparatus that implants ions as impurities into a semiconductor wafer, etc., is equipped with a predetermined raw material gas (
An ion source is provided for generating desired ions from solid raw materials (or solid raw materials).

As such an ion source, a so-called electron beam excitation ion source is known, which generates ions by irradiating a predetermined raw material gas with electrons.

(Problems to be Solved by the Invention) In the electron beam-excited ion source, the filament is sputtered by plasma (ions) and is worn out, so it is necessary to periodically replace the filament. Therefore, it is desired to further extend the life of the filament, reduce the frequency of maintenance, and improve productivity.

The present invention has been made in response to such conventional circumstances, and is capable of producing ions that can extend the life of the filament compared to the conventional method, reduce the maintenance opening degree, and improve productivity. It is intended to provide a method.

[Structure of the Invention] (Means for Solving the Problems) That is, the present invention introduces a discharge gas into a filament atmosphere, turns the discharge gas into plasma, and irradiates the raw material gas for ion generation with electrons in the plasma. In the ion generation method for generating ions from this raw material gas, the filament is heated by supplying an alternating current to the filament.

(Function) In the ion generation method of the present invention having the above configuration, when the discharge gas is turned into plasma and electrons for irradiating the source gas are generated, an alternating current is supplied to the filament to heat it.

Therefore, compared to the conventional method of heating the filament by passing a direct current through the filament, consumption of the filament by sputtering or the like can be made more uniform, and the life of the filament can be prolonged compared to the conventional method.

That is, when turning discharge gas into plasma, the main factor that determines filament consumption is sputtering caused by the electric potential formed between the plasma potential and the filament. When a filament is heated with a direct current as in the past, an electric potential is always generated along the length of the filament, so the electric potential formed between the plasma potential and the filament is There is always a difference along the length.

Therefore, the filament wears out unevenly in the length direction, and the negative side of the filament wears out locally, resulting in a significantly shortened filament life.

However, when a filament is heated with an alternating current (for example, one with a frequency of 50 to 60 or higher, which is currently used in Japan), an electric current is generated along the length of the filament. Because the potential is alternately changed by the frequency of the alternating current, the difference in electrical potential (in the length direction of the filament) that occurs with conventional direct current heating is different from the electrical potential formed between the plasma potential and the filament. (difference in electrical potential that occurs along the line) is canceled out. Therefore, the wear of the filament can be made uniform, and by extending the life of the filament compared to the conventional method, it is possible to reduce the degree of opening for maintenance and improve productivity.

(Example) Embodiments of the method of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, an electron generation chamber 2 formed in the shape of a rectangular container with each side having a length of, for example, several centimeters is provided above the ion source 1. The electron generating chamber 2 is made of a conductive material with a high melting point, such as molybdenum, and is made of an insulating material with a high melting point (for example, a melting point of 1200° C. or higher), such as SiN4, so as to close the opening provided on the side surface of the electron generating chamber 2.
, BN or the like is provided. and,
A U-shaped filament 4 made of a conductive high melting point material such as tungsten is provided on the insulating plate 3 so as to project into the electron generating chamber 2 with its both ends supported.

Furthermore, a discharge gas inlet 5 is provided in the upper part of the electron generation chamber 2 to introduce a discharge gas such as argon (Ar) gas to generate plasma and generate electrons. On the other hand, in the lower part of the electron generation chamber 2, a circular hole 6 is provided for extracting electrons from the plasma generated within the electron generation chamber 2.

Further, a plate-shaped insulating member 8 is provided at the lower part of the electron generating chamber 2 so as to form a bottleneck 7 continuous with the circular hole 6. An electron extraction electrode 10 having a through hole 9 is provided.

An insulating member 11 is provided below the electron extraction electrode 1o.
The ion generation chamber 12 is connected via the ion generation chamber 12. The ion generation chamber 12 is formed into a container shape from a conductive high melting point material such as molybdenum, and the inside thereof has a cylindrical shape with both a diameter and a height of about several centimeters. Further, a bottom plate 14 is fixed to the bottom of the ion generation chamber 12 via an insulating member 13.

Furthermore, a source gas inlet 15 is provided on the side surface of the ion generation chamber 12 for introducing a source gas such as BF3 into the ion generation chamber 12 to generate desired ions. An ion extraction slit 16 is provided at a position facing the introduction port 15.

Furthermore, in this embodiment, an inner tube 17 is provided within the ion generation chamber 12. This inch cylinder 17 is made of a material that is difficult to resist the effects of plasma (sputtering, etching, etc.), such as ceramic and sox.
It is configured to cover the metal surface within the ion generation chamber 12 and protect it from plasma.

In this embodiment, using the electron beam excitation ion source having the above configuration, desired ions are generated in the following manner.

That is, by a magnetic field generating means (not shown), the arrow B shown in the drawing is
A magnetic field is applied to guide the electrons in the electron extraction direction as indicated by z. Then, an alternating current voltage Vr is applied to the filament 4 to heat it, and a discharge voltage Vd is applied to the electron generation chamber 2 through a resistor R to the filament 4, and a discharge voltage Vd is applied to the electron extraction electrode 10.
is applied, and an accelerating voltage Va is applied between the electron extraction electrode ] 0 and the ion generation chamber 12 .

Then, a discharge gas such as argon gas is introduced into the electron generation chamber 2 from the discharge gas inlet 5 at a predetermined flow rate of 0.05, for example.
It is introduced at 3 CCM or more, and a discharge is caused by a discharge voltage Vd to generate plasma. Then, the electrons in this plasma pass through the circular hole 6, the bottleneck 7, and the through hole 9 of the electron extraction electrode 10, and enter the ion generation chamber 12.
drawn inside.

On the other hand, a predetermined raw material gas is supplied into the ion generation chamber 12 from the raw material gas inlet 15 at a predetermined flow rate of, for example, 0.153 CC.
The gas is introduced at M or more to create a predetermined raw material gas atmosphere.

Therefore, the electrons flowing into the ion generation chamber 12 are accelerated by the accelerating electric field, collide with source gas molecules, and generate dense plasma. Then, ions in the plasma are extracted from the ion extraction slit 16 by an ion extraction electrode (not shown) and irradiated onto a semiconductor wafer or the like as a desired ion beam, for example.

That is, in the ion generation method of this embodiment, an alternating current voltage r is applied to the filament 4, and the filament 4 is heated by the alternating current. Then, by applying a DC discharge voltage Vd between the filament 4 and the electron generation chamber 2, a discharge gas such as argon gas introduced into the electron generation chamber 2 from the discharge gas inlet 5 is generated into a plasma. become

Therefore, the consumption of the filament 4 is made more uniform compared to the case where the filament 4 is heated by direct current.

In other words, the filament 4 is mainly consumed by sputtering by ions (for example, argon ions) in the plasma generated by discharge, but when the filament 4 is heated by direct current, an electric potential is generated along the length of the filament 4. The plasma is unevenly distributed according to this potential gradient, and sputtering is concentrated at this location (the negative side of the filament 4). On the other hand, when the filament 4 is heated with an alternating current as in this embodiment, the electric potential changes alternately depending on the frequency, so the plasma moves and sputtering occurs uniformly.

Therefore, the life of the filament 4 can be extended compared to the case where the filament 4 is heated by direct current, and the frequency of maintenance can be reduced to improve productivity.

The frequency of the alternating current may be, for example, the frequency 50 to 60 (2) currently used in Japan, but it may be a frequency higher than that.

Furthermore, by making the plasma density uniform within the electron generation chamber 2 in which the filament 4 is accommodated, it becomes possible to reduce the diameter of the hole 7. By reducing the hole diameter of the bottleneck 7, the pressure inside the electron generation chamber 2 increases, so that plasma can be maintained even if the discharge gas flow rate is lowered.

By lowering the discharge gas flow rate, it is possible to reduce the amount of discharge gas that flows into the ion generation chamber 12 without participating in discharge. Therefore, the probability that electrons collide with discharge gas molecules and are consumed in the ion generation chamber 12 can be reduced, and the electrons and source gas can be efficiently collided to obtain, for example, multivalent ions. I can do it.

In addition, by reducing the hole diameter of the bottleneck 7, electrons converge inside the bottleneck 7 and pass through the bottleneck 7 better, so that the transmittance of electrons passing through the hole 9 of the electron extraction electrode 10 (I a /Id) increases. By increasing the thickness of the bottleneck 7 to account for this increased ratio, it is necessary to increase Id, the denominator of the electron transmittance, and make the transmittance about 20%, so the thickness of the bottleneck 7 is increased. By doing so, the life of the bottleneck 7 can be extended.

As mentioned above, the plasma in the electron generation chamber 2 is moved by the alternating current electric field, but the plasma in the ion generation chamber 12 is hardly affected by this alternating electric field, so the uniformity of the extracted ions is impaired. Never.

[Effects of the Invention] As explained above, according to the ion generation method of the present invention, the life of the filament can be extended compared to the conventional method, and the maintenance opening degree can be reduced to improve productivity. I can do it.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an ion source for explaining a method according to an embodiment of the present invention. 1... Ion source, 2... Electron generation chamber,
3... Insulating plate, 4... Filament,
5... Gas inlet for discharge, 6... Circular hole, 7... Bottle, 8... Insulating member, 9
...Through hole, 10...Electron extraction electrode, 11...Insulating member, 12...Ion generation chamber, 13...Insulation Sexual member, 14...
...Bottom plate, 15... Raw material gas inlet, 16...
...Slit for extracting ions, 17...
inner tube.

Claims (1)

[Claims] (1) In an ion generation method in which a discharge gas is introduced into a filament atmosphere, the discharge gas is turned into plasma, electrons in the plasma are irradiated to a raw material gas for ion generation, and ions are generated from this raw material gas, the filament is An ion generation method characterized by heating by supplying an alternating current.