JPH03210743A - Ion source - Google Patents

Abstract

PURPOSE:To reduce the frequency of maintenance, and to improve the operation rate of an ion source device by providing a mechanism that forms a shade to a plasma so as to suppress the adhesion of a flying material, at least on a part of the insulating member of the ion source. CONSTITUTION:When an electron deriving electrode 8, an insulating plate 12, and a conductive plate 13 are combined together, a contact part 19 of the plate 12 and the plate 13 forms a shadow to the plasma in an ion generating chamber, due to a protruded part 16. The consumption of the electrode 8 by the effect of the plasma is prevented by an electrode protecting mechanism 11, while the plate 13, which is a member located where the consumption most likely occurs, is formed independently of the plate 12 and the electrode 8, so as for only the plate 13 is to be replaced at the time of consumption. In this ion source, the mechanism of suppressing the adhesion of flying material by forming the shadow toward the plasma, is provided on the contact part of the electrode 8 and the plasma 12, and on the contact part of a bottom plate 24 of an ion generating chamber 20 and an insulating member 23, whereby the flying material is hard to adhere to these contact parts. Productivity can thus be improved.

Description

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

(Prior Art) Generally, an ion source is placed in, for example, an ion implanter that implants ions as impurities into a semiconductor wafer.

Conventionally, such an ion source is an ion source that generates plasma from a predetermined gas by applying a voltage between a filament and an anode electrode, and extracts desired ions from this plasma for use, such as a Freeman type ion source. ion sources are often used.

In addition, as the ion source, a voltage is applied between the filament and the anode electrode to generate a first plasma from a predetermined discharge gas, and electrons are extracted from the first plasma and introduced into the ion generation chamber. There is an electron beam excitation ion source that generates desired ions (second plasma) by irradiating a predetermined raw material gas. Such an ion source is characterized by being able to obtain high ion current density with low ion energy.

In the above ion source, the chamber such as the ion generation chamber is
It is composed of a conductive member and an insulating member interposed between the conductive members to maintain electrical insulation between the conductive members. In such an ion source, the conductive member is scraped by plasma action such as etching, sputtering, etc.
As it wears out, these scraped flying objects adhere to, for example, the surface of the insulating member and form a conductive film, causing insulation failure. Therefore, conventionally, ion sources have been regularly subjected to maintenance such as removal of such conductive deposits.

(Problem to be solved by the invention) However, with conventional ion sources, maintenance such as removing conductive deposits as described above must be performed frequently, for example, every few hours of use. Ta. Further, for example, in an ion implantation device or the like, such maintenance requires a long time since the high vacuum chamber is once returned to normal pressure. For this reason, there was a problem in that the operating rate of the ion implanter and the like was significantly lowered, leading to deterioration of productivity.

The present invention has been made in response to such conventional circumstances, and provides an ion source that can reduce the frequency of maintenance compared to the past, improve the operating rate of the device, and improve productivity. This is what we are trying to provide.

[Structure of the Invention] (Means for Solving the Problems) That is, the ion source of the present invention irradiates a predetermined raw material gas with electrons to generate plasma in a chamber composed of a conductive member and an insulating member. The ion source that generates ions is characterized in that at least a portion of the insulating member is provided with a mechanism that forms a shadow against the plasma to suppress adhesion of flying objects.

(Function) In the ion source of the present invention having the above configuration, at least a part of the insulating member constituting the chamber, for example, the contact portion between the electron extraction electrode and the insulating member covering the lower surface of the electron extraction electrode, or the ion generation A mechanism is provided at the contact portion between the bottom plate of the chamber and the insulating member that holds the bottom plate to form a shadow against the plasma to suppress the adhesion of flying objects.

Therefore, the frequency of maintenance such as removal of conductive deposits can be reduced compared to the conventional method, and the operating rate of the apparatus can be improved to improve productivity.

(Example) Hereinafter, an example in which the present invention is applied to an electron beam excited ion source will be described with reference to the drawings.

As shown in FIG. 1, the electron generation chamber 1 is formed of a conductive high melting point material such as molybdenum into a rectangular container shape with each side having a length of, for example, several centimeters.

Further, an opening is provided on one side of the electron generation chamber 1, and a 513N4, for example, 513N4
A heat-resistant insulating member 2 formed in a plate shape made of , BN, or the like is provided, and the electron generation chamber 1 is configured to be airtight.

Further, the insulating member 2 is provided with a U-shaped filament 3 made of a high melting point material such as tungsten and protruding into the electron generating chamber 1.

Further, in the upper part of the electron generation chamber 1, a gas such as argon (Ar) is provided to generate plasma and generate electrons.
A discharge gas introduction hole 4 for introducing a discharge gas such as gas is provided at the bottom of the electron generation chamber 1. For example, a circular hole 5 of several millimeters is provided.

In addition, in the lower part of the electron generation chamber 1, for example, S i 3 N 4, BN
An insulating member 7 made of the like is provided, and an electron extraction electrode 8 is provided at the bottom of this insulating member 7.

As shown in FIG. 2, the electron extraction electrode 8 is made of a high melting point material such as tungsten and has a plate shape. Further, an electron beam passage hole 9 with a diameter of, for example, about 2 to 3 mm is formed in this electron extraction electrode 8 in correspondence with the aforementioned bottleneck 6, and a gas vent is formed surrounding the electron beam passage hole 9. A plurality (for example, eight) of holes 10 (holes with a diameter of, for example, about 1 to 2 square centimeters) are formed.

Furthermore, an electrode protection mechanism 11 is provided below the electron extraction electrode 8 to cover the lower surface of the electron extraction electrode 8 and prevent the electron extraction electrode 8 from being worn out by etching, sputtering, or the like. This electrode protection mechanism 11 is shown in FIGS.
As shown in the figure, it is composed of an insulating plate 12 made of, for example, insulating ceramics, and a conductive plate 13 made of, for example, conductive ceramics. Here, the conductive plate 13 may be made of insulating ceramics or the like.

That is, the insulating plate 12 covers the lower surface side of the electron extracting electrode 8 and has a substantially similar outer shape to the electron extracting electrode 8 so as to protect the electron extracting electrode 8 from the action of plasma. A recessed portion 14 into which the conductive plate 13 is fitted is formed. Moreover, in this recessed part 14,
A circular hole 15 is provided to form an opening corresponding to the electron beam passage hole 9 and the gas vent hole 10 of the electron extraction electrode 8.A circular hole 15 is provided around the circular hole 15 to form an opening corresponding to the electron beam passage hole 9 and the gas vent hole 10. A protrusion 16 is formed.

On the other hand, the conductive plate 13 is made of a material that is less abrasive due to the action of plasma, such as conductive ceramics.
It is configured in a shape corresponding to 4. Further, in this conductive plate 13, through holes 17 are formed to correspond to the electron beam passage holes 9 and gas vent holes 10 of the electron extraction electrode 8 and have substantially the same diameter as these holes. Furthermore, a circular concave portion 18 having a larger diameter than the protruding portion 16 of the insulating plate 12 is formed on the lower surface of the conductive plate 13 . Here, since the conductive plate 13 is made of conductive ceramics, the electron extraction electrode 8 and the conductive plate 13 may be integrated.

As shown in FIG. 5, when the electron extracting electrode 8, the insulating plate 12, and the conductive plate 13 are combined, the protruding portion 16 forms a contact portion 19 between the insulating plate 12 and the conductive plate 13, which will be described later. It is configured to cast a shadow on the plasma inside the ion generation chamber.

The electrode protection mechanism 11 is intended to prevent the electron extraction electrode 8 from being worn out due to the action of plasma, as described above. Further, the conductive plate 13 is a member located at the part that is most subject to wear and tear, and is constructed separately from the insulating plate 12 and the electron extraction electrode 8 so that only the conductive plate 13 can be replaced when it wears out. There is. Further, the conductive plate 13 is not limited to conductive ceramics, but may be made of other metals or insulating materials as long as the material is less abrasive due to the action of plasma.

An ion generation chamber 20 is provided below the electron extraction electrode 8 and the electrode protection mechanism 11.

The ion generation chamber 20 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, for example, both a diameter and a height of several centimeters.

Note that the shape of the ion generation chamber 20 may be other than a cylindrical shape, such as a rectangle, but a cylindrical shape is preferable from the viewpoints of workability, ease of cleaning, improvement of plasma density, and the like.

Further, a source gas inlet 21 is provided on the side surface of the ion generation chamber 20 for introducing a source gas such as BF3 into the ion generation chamber 20 to generate desired ions. An ion extraction slit 22 is provided so as to face the gas introduction port 21 .

Furthermore, an insulating member 23 is provided at the bottom of the ion generation chamber 20.
The side wall of the ion generation chamber 20 is connected to the switch S via
A bottom plate 24 made of, for example, a conductive material with a high melting point is fixed in a state where a negative potential is applied by Vc or a power source Vc, and in an electrically isolated state (floating state). is charged and configured to reflect electrons.

Further, as shown in FIG. 6, the bottom plate 24 is formed into a cylindrical shape having a flange 25 at the bottom, and an annular groove 26 is formed on the upper surface of the flange 25. As shown in FIG.

On the other hand, the insulating member 23 has an opening 2 corresponding to the bottom plate 24.
7 is formed, and the inside thereof is formed into a step-like shape. The bottom plate 24 is held at the outer periphery of the flange 25 and is configured to cover the upper surface of the flange 25 and approximately the center of the groove 26 to form a shadow against the plasma.

In the electron beam excited ion source of this embodiment with the above configuration,
Desired ions are generated in the following manner while applying a magnetic field for guiding electrons in the vertical direction as indicated by an arrow Bz in the figure by a magnetic field generating means (not shown).

That is, while applying a filament voltage vf to the filament 3 and heating it with electricity, a discharge voltage Vd is applied to the electron generation chamber 1 through a resistor R, and a discharge voltage Vd is applied to the electron extraction electrode 8. Then, an accelerating voltage Va is applied between the electron extraction electrode 8 and the ion generation chamber 20.

Then, a discharge gas such as argon gas is introduced into the electron generation chamber 1 from the discharge gas introduction hole 4 at a predetermined flow rate of 0.05, for example.
It is introduced at 8 CCM or more, and a discharge is caused by a discharge voltage Vd to generate plasma. Then, the electrons in the plasma pass through the circular hole 5, the bottleneck 6, and the electron beam passage hole 9 of the electron extraction electrode 8, and are extracted into the ion generation chamber 20 by the accelerating voltage Va.

On the other hand, a predetermined raw material gas, for example, BF3, is introduced into the ion generation chamber 20 from the raw material gas inlet 21 at a predetermined flow rate, for example, 0.
．． The ion generation chamber 20 is introduced at a predetermined pressure of 158 CCM or more, for example, 0.001 to 0.02 Torr.
The raw material gas atmosphere is set to r.

Therefore, the electrons flowing into the ion generation chamber 20 are accelerated by the accelerating electric field, collide with the BF3, and generate dense plasma. And ion extraction slit 22
Ions are extracted from this plasma and used, for example, as a desired ion beam for ion implantation into semiconductor wafers.

At this time, each member constituting the ion source, such as molybdenum constituting the ion generation chamber 20, is consumed by etching etc. under the action of the plasma, and the scraped flying objects are removed from the surface of other members, such as the insulating member. be coated on. Therefore, a conductive film is formed on the surface of the insulating member.

However, in the ion source of this embodiment, as shown in FIG. 5 and FIG. A mechanism is provided at the contact area between the bottom plate 24 of 20 and the insulating member 23 to suppress the adhesion of flying objects by forming a shadow against the plasma. It is configured.

Therefore, the time it takes for a flying object to go around and adhere to the above-mentioned part, that is, the above-mentioned contact part, a conductive film is formed, the conductive members are electrically connected, and an insulation failure occurs. It can last much longer than conventional methods, and the frequency of maintenance can be significantly reduced compared to conventional methods.

Note that the mechanism for suppressing the adhesion of flying objects by forming a shadow on the plasma is not limited to the structure of the above embodiment, and various modifications are possible.

Furthermore, the installation position is not limited to the above-mentioned contact portions, but may be installed at any location where there is a possibility of insulation failure due to adhesion of flying objects.

[Effects of the Invention] As explained above, according to the ion source of the present invention, the frequency of maintenance can be reduced compared to the conventional one, and the operating rate of the device can be improved, and productivity can be improved. .

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an electron beam excited ion source according to an embodiment of the present invention, FIG. 2 is a diagram showing the electron extracting electrode in FIG. 1, and FIG. 3 is a diagram showing the insulation of the electrode protection mechanism in FIG. 1. Diagram showing the sexual plate,
4 is a diagram showing the conductive plate of the electrode protection mechanism in FIG. 1, FIG. 5 is a diagram showing a cross section of the electron extraction electrode and electrode protection mechanism in FIG. 1, and FIG. 6 is a diagram showing the bottom plate and It is a figure which shows the insulating member which holds a bottom plate. DESCRIPTION OF SYMBOLS 1... Electron generation chamber, 2... Insulating member, 3... Filament, 4... Gas introduction hole for discharge, 5...・Circular hole, 6... bottleneck, 7... insulating member, 8... electron extraction electrode, 9... electron beam passing hole, 10...・・・
... Gas vent hole, 11 ... Electrode protection mechanism, 12
...Insulating board, 13... Conductive board, 1
4... Concave portion, 15... Circular hole, 16.
...Protrusion, 17...Through hole, 18...
...Circular recessed part, 19...Contact part, 20...
...Ion generation chamber, 21 ... Raw material gas inlet, 22 ... Ion extraction slit, 23
...Insulating member, 24 ... Bottom plate, 25
...Flange, 26...Groove.

Claims (3)

[Claims] (1) In an ion source that irradiates a predetermined raw material gas with electrons to generate plasma and generate ions in a chamber composed of a conductive member and an insulating member, at least a portion of the insulating member An ion source comprising a mechanism for forming a shadow on the plasma to suppress adhesion of flying objects. (2) The ion source according to claim 1, wherein the mechanism for suppressing adhesion of flying objects is provided at a contact portion between an electron extraction electrode and an insulating member covering a lower surface of the electron extraction electrode. . (3) The ion structure according to any one of claims 1 to 2, wherein the mechanism for suppressing adhesion of flying objects is provided at a contact portion between a bottom plate of the ion generation chamber and an insulating member that holds this bottom plate. source.