JP2889930B2 - Ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to an ion source.

(Prior Art) Generally, an ion source is arranged in, for example, an ion implantation apparatus for implanting ions as impurities into a semiconductor wafer.

Conventionally, as such an ion source, an ion source that generates a plasma from a predetermined gas by applying a voltage between a filament and an anode electrode, and extracts and uses desired ions from the plasma, for example, a Freeman type Are widely used.

In addition, as the above-mentioned ion source, a voltage is applied between the filament and the anode electrode, and a first discharge gas is supplied from the predetermined discharge gas.
Is generated by extracting electrons from the first plasma and irradiating a predetermined source gas introduced into the ion generation chamber with desired ions (second plasma).
There is an electron beam excited ion source for generating the ion beam. Such an ion source is characterized in that a high ion current density can be obtained with low ion energy.

In the above-mentioned ion source, a chamber such as an ion generating chamber is formed of a conductive member and an insulating member interposed between the conductive members and maintaining electrical insulation between the conductive members. In such an ion source, the conductive member is shaved by the action of plasma, such as etching and sputtering, and is consumed, and these shaved flying objects are adhered to, for example, the surface of the insulating member to form a conductive material. Forming a film,
Causes insulation failure. Therefore, conventionally, in the ion source, maintenance such as removal of such a conductive adhered substance is regularly performed.

(Problems to be Solved by the Invention) However, in the conventional ion source, it has been necessary to frequently perform maintenance such as removal of the conductive adherend as described above, for example, every several hours of use. In addition, for example, in an ion implantation apparatus or the like, such maintenance is performed by once returning the high vacuum chamber to normal pressure.
It takes a long time. For this reason, there has been a problem that the operation rate of the ion implantation apparatus and the like is significantly reduced, and the productivity is deteriorated.

The present invention has been made in view of such a conventional situation, and an ion source capable of reducing the maintenance frequency, improving the operation rate of the apparatus, and improving the productivity as compared with the related art. It is something to offer.

[Constitution of the Invention] (Means for Solving the Problems) That is, according to the present invention, in a chamber, a predetermined source gas is irradiated with electrons extracted by an electron extraction electrode to generate plasma to generate ions. A source, comprising: a conductive member constituting the electron extraction electrode; and an insulating surface provided so as to cover a surface of the conductive member where electrons are extracted and the plasma is generated, and which is exposed in the chamber. At least a part of the contact portion with the conductive member, the conductive member is configured such that the end of the insulating member extending from the contact portion covers a surface near the contact portion with a gap provided therebetween, An ion source provided with a mechanism for suppressing the attachment of flying objects from the plasma to the contact portion.

(Operation) In the ion source of the present invention having the above-described configuration, at least a part of the insulating member constituting the chamber, for example, a contact portion between the electron extracting electrode and the insulating member covering the lower surface of the electron extracting electrode,
Alternatively, a mechanism is provided at a contact portion between the bottom plate of the ion generation chamber and an insulating member holding the bottom plate, for example, to form a shadow on the plasma to suppress the attachment of flying objects.

Therefore, the frequency of maintenance such as removal of the conductive adherend can be reduced as compared with the related art, so that the operation rate of the apparatus can be improved and the productivity can be improved.

(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 generating chamber 1 is formed of a conductive high melting point material such as molybdenum into a rectangular container having a length of about several centimeters on each side. An opening is provided on one side surface of the electron generating chamber 1, and a heat-resistant insulating member formed in a plate shape made of, for example, Si ₃ N ₄ or BN so as to close the opening. 2 are provided, and the electron generation chamber 1 is airtightly configured.

The insulating member 2 is provided with, for example, a U-shaped filament 3 made of a material having a high melting point, such as tungsten, so as to protrude into the electron generation chamber 1.

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

An insulating member 7 made of, for example, Si ₃ N ₄ , BN or the like is provided below the electron generating chamber 1 so as to form a bottleneck 6 continuously with the circular hole 5. Is provided with an electron extraction electrode 8 below.

As shown in FIG. 2, the electron extraction electrode 8 is formed in a plate shape from a high melting point material, for example, tungsten.
The electron extraction electrode 8 is formed with an electron beam passage hole 9 having a diameter of, for example, about 2 to 3 mm, corresponding to the bottleneck 6 described above. A plurality (for example, eight) of holes 10 (holes having a diameter of, for example, about 1 to 2 mm) are formed.

Further, 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 consumed by etching, sputtering, or the like. The electrode protection mechanism 11 includes, as shown in FIGS. 3 to 5, an insulating plate 12 made of, for example, insulating ceramics and a conductive plate 13 made of, for example, conductive ceramics. .

That is, the insulating plate 12 has substantially the same outer shape as the electron extraction electrode 8 so as to cover the lower surface of the electron extraction electrode 8 and protect the electron extraction electrode 8 from the action of plasma. In the figure, a concave portion 14 for fitting the conductive plate 13 is formed. The recess 14 is provided with a circular hole 15 for forming an opening corresponding to the electron beam passage hole 9 and the gas vent hole 10 of the electron extraction electrode 8. Is formed with an annular protrusion 16 protruding upward.

On the other hand, the conductive plate 13 is made of a material that is less consumed by the action of plasma, for example, conductive ceramics.
It is configured in a shape corresponding to. Also, this conductive plate
In the hole 13, a through hole 17 having substantially the same diameter as these holes is formed corresponding to the electron beam passage hole 9 and the gas vent hole 10 of the electron extraction electrode 8. Further, on the lower surface of the conductive plate 13, a circular concave portion 18 having a larger diameter than the protrusion 16 of the insulating plate 12 is formed. Here, since the conductive plate 13 uses conductive ceramics, the electron extraction electrode 8 and the conductive plate 13 may be integrated.

Then, as shown in FIG. 5, when the electron extraction electrode 8, the insulating plate 12, and the conductive plate 13 are combined, the projecting portion 16 causes the contact portion 19 between the insulating plate 12 and the conductive plate 13 to be described later. It is configured to have a shadow on the plasma in the ion generation chamber.

The electrode protection mechanism 11 is for preventing the electron extraction electrode 8 from being consumed by the action of the plasma as described above. Further, the conductive plate 13 is a member located at a site where the wear is most severe, and is configured separately from the insulating plate 12 and the electron extraction electrode 8 so that only the conductive plate 13 can be replaced at the time of wear. I have. Also, this conductive plate 13
The material is not limited to conductive ceramics as long as the material is less consumed by the action of plasma, and may be made of other metals or insulating materials.

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 in a container shape from a conductive high melting point material, for example, molybdenum, and the inside thereof has a cylindrical shape having a diameter and a height of about several centimeters, for example.

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

Further, the side surfaces of the ion generation chamber 20 is the source gas inlet 21 is provided for introducing a material gas, such as BF ₃ or the like for generating the desired ions in the ion generation chamber 20, the An ion extraction slit 22 is provided so as to face the source gas inlet 21.

Further, a state in which a negative potential is applied to the bottom of the ion generation chamber 20 via a switch Sc or a power supply Vc from the side wall of the ion generation chamber 20 via an insulating member 23, and a state in which the negative side is electrically isolated. In a (floating state), a bottom plate 24 made of, for example, a high melting point conductive material is fixed, and the bottom plate 24 is configured to be charged by electron irradiation and reflect electrons.

As shown in FIG. 6, the bottom plate 24 is formed in a columnar shape having a flange 25 on the bottom, and an annular groove 26 is formed on the upper surface of the flange 25. on the other hand,
An opening 27 corresponding to the bottom plate 24 is formed in the insulating member 23, and the inside thereof is formed in a step shape. And
The bottom plate 24 is held by the outer peripheral portion of the flange 25, and covers the upper surface of the flange 25 and the substantially central portion of the groove 26 so as to form a shadow on the plasma.

In the electron beam excited ion source of this embodiment having the above-described configuration, a desired ion is applied as follows in a state where a magnetic field for guiding electrons in a vertical direction as shown by an arrow Bz is applied by a magnetic field generating means (not shown). Generate.

That is, a filament voltage Vf is applied to the filament 3 to heat it, and a discharge voltage Vd is applied to the filament 3 through the resistor R to the electron generating chamber 1 and a discharge voltage Vd is applied to the electron extraction electrode 8. Then, an acceleration voltage Va is applied between the electron extraction electrode 8 and the ion generation chamber 20.

Then, from the discharge gas introduction hole 4 into the electron generation chamber 1,
Discharge gas, for example, argon gas at a predetermined flow rate, for example, 0.05 SC
Introduced at CM or higher, discharge is generated by the discharge voltage Vd, and plasma is generated. Then, the electrons in the plasma are extracted into the ion generation chamber 20 through the circular hole 5, the narrow path 6, and the electron beam passage hole 9 of the electron extraction electrode 8 by the acceleration voltage Va.

On the other hand, inside the ion generation chamber 20, a predetermined source gas, for example, BF ₃ is previously supplied from the source gas inlet 21 at a predetermined flow rate, for example, 0.15SCC.
It is introduced at a pressure of M or more, and the inside of the ion generation chamber 20 is kept at a predetermined pressure, for example, a source gas atmosphere of 0.001 to 0.02 Torr.

Therefore, the electrons flowed into the ion generation chamber 20 are accelerated by the acceleration electric field, collide with BF _3, to generate a dense plasma. Then, the ions are extracted from the plasma by the ion extracting slit 22 and used as, for example, a desired ion beam for ion implantation into a semiconductor wafer.

At this time, each member constituting the ion source, for example, molybdenum or the like constituting the ion generation chamber 20 is consumed by the etching or the like under the action of the plasma, and the cut-off flying material becomes a surface of another member, for example, an insulating member. To adhere. Therefore, a conductive film is formed on the surface of the insulating member.

However, in the ion source of this embodiment, as shown in FIGS. 5 and 6, the electron extraction electrode 8 (conductive plate) is used.
A mechanism for forming a shadow on the plasma and suppressing the attachment of a flying object is provided at a contact portion between the insulating plate 12 and the insulating plate 12 and a contact portion between the bottom plate 24 of the ion generation chamber 20 and the insulating member 23. It is configured such that flying objects are not easily attached to these contact portions.

Therefore, the flying object wraps around and adheres to the shadow area, that is, the contact portion, and a conductive film is formed, the conductive members are electrically connected to each other, and a time until an insulation failure occurs is reduced. It can be much longer than before,
The maintenance frequency can be greatly reduced as compared with the conventional case.

The mechanism for forming a shadow on the plasma to suppress the attachment of the flying object is not limited to the structure of the above embodiment, and various modifications are possible. In addition, the installation position is not limited to the above-described contact portions, and may be provided at any location where insulation failure may occur due to the attachment of a flying object.

[Effects of the Invention] As described above, according to the ion source of the present invention, the frequency of maintenance can be reduced as compared with the related art, the operation rate of the apparatus can be improved, and the productivity can be improved. .

[Brief description of the drawings]

FIG. 1 is a view showing a configuration of an electron beam excited ion source according to one embodiment of the present invention, FIG. 2 is a view showing an electron extraction electrode of FIG. 1, and FIG. 3 is an insulation of an electrode protection mechanism of FIG. FIG. 4 is a view showing a conductive plate of the electrode protection mechanism of FIG. 1, FIG. 5 is a view showing a cross section of the electron extraction electrode and the electrode protection mechanism of FIG. 1, and FIG. FIG. 2 is a view showing a bottom plate and an insulating member holding the bottom plate of FIG. 1; DESCRIPTION OF SYMBOLS 1 ... Electron generation chamber, 2 ... Insulating member, 3 ... Filament, 4 ... Discharge gas introduction hole, 5 ... Circular hole, 6 ... Bottleneck, 7 ... Insulating member, 8 ... Electron Extraction electrode, 9: electron beam passage hole, 10: gas vent hole, 11: electrode protection mechanism, 12: insulating plate, 13: conductive plate, 14: concave portion,
15 ... circular hole, 16 ... projecting part, 17 ... through hole, 18 ... circular concave part, 19 ... contact part, 20 ... ion generation chamber, 21 ... source gas inlet, 22 ... ion Drawer slit, 23 ……
Insulating member, 24 bottom plate, 25 flange, 26 groove.

Claims (1)

(57) [Claims] 1. An ion source for irradiating a predetermined raw material gas with electrons extracted by an electron extraction electrode in a chamber to generate plasma to generate ions, wherein: a conductive member constituting the electron extraction electrode; At least a portion of a contact portion with an insulating member having an exposed surface that is provided to cover a surface on which the plasma is generated by extracting electrons of the conductive member and is exposed in the chamber, the conductive member includes: The end of the insulating member extending from the contact portion covers the surface of the member in the vicinity of the contact portion, with an end provided with a gap, thereby preventing the flying object from the plasma from adhering to the contact portion. An ion source, characterized in that it has a mechanism for performing ionization.