Ion source and repeller structure

1. An ion source comprising:

a plasma generating chamber configured to serve as a container for generating therein a plasma and as an anode, while allowing a source gas to be introduced therein;

a cathode provided in the plasma generating chamber and configured to emit electrons for ionizing the source gas to generate the plasma; and

a repeller structure disposed in opposed relation to the cathode within the plasma generating chamber to reflect the electrons toward the cathode, wherein the repeller structure comprises:

a target member configured to be sputtered by the plasma to emit given ions, and provided with a through-hole penetrating between a sputterable surface and a reverse surface thereof; and

a repeller body which supports the target member while being inserted in the through-hole of the target member, and has a repeller surface exposed on the side of the sputterable surface through the through-hole, the target member directly contacting the repeller body and being electrically conductive with respect to each other, and wherein a center of an electron emitting portion of the cathode and a center of the repeller surface are located approximately coaxially with each other, and

wherein the target member is made of a material selected from the group consisting of gallium oxide, gallium nitride, gallium phosphide, gallium arsenide and gallium fluoride, and a magnet is provided outside the plasma generating chamber to generate a magnetic field along a line that, connects the cathode to the repeller structure positioned in the plasma generating chamber, the magnetic field being parallel to a plasma generating chamber axis, so as to cause electrons to move back and forth between the cathode and the repeller while circling the magnetic field, with the direction of the magnetic field as its rotating axis, and

further wherein the plasma generating chamber is provided with an ion extraction port arranged on the plasma generating chamber parallel to the plasma generating chamber axis.

2. The ion source as defined in claim 1 , wherein:

the target member has a counterbored portion formed by diametrically expanding an opening region of the through-hole on the side of the sputterable surface; and

the repeller body has a large-diameter portion formed at a distal end thereof and engageable with the counterbored portion,

wherein, under a condition that the large-diameter portion is engaged with the counterbored portion, the target member is supported by the repeller body, and a distal edge surface of the large-diameter portion is the repeller surface.

3. The ion source as defined in claim 2 , wherein, under the condition that the engageable portion is engaged with the counterbored portion, the sputterable surface is located on the side of the cathode with respect to the repeller surface.

4. The ion source as defined in claim 2 , wherein the repeller body has a threaded portion on an outer peripheral surface thereof, and wherein a nut member is screwed onto the threaded portion from the side of the reverse surface of the target member, so that the target member is fixedly clamped by the large-diameter portion and the nut member.

5. The ion source as defined in claim 1 , wherein the target member has a generally circular disk shape, and wherein the through-hole is formed in an approximately central region of the target member.

6. The ion source as defined in claim 1 , wherein the sputterable surface of the target member includes a concave tapered surface or a concave curved surface, which is annularly formed about the through-hole.

7. The ion source as defined in claim 1 , wherein the source gas is phosphorus fluoride or boron fluoride.