Fast atom beam source

Abstract: A fast atom beam source which is capable of emitting a fast atom beam with low energy efficiently and which enables a reduction in the overall size of the apparatus. A reaction gas mixed with a halogen or a halide is introduced into a fast atom beam source casing through a plate-shaped anode (4), and gas ions that are produced by a plasma discharge induced at a relatively low discharge voltage are converted into a fast atom beam, which is emitted from fast atom beam emitting holes provided in a plate-shaped cathode (21) that is disposed to face opposite to the anode.

Description: The present invention relates to a fast atom beam source and, more particularly, to a fast atom beam source structure that is capable of emitting a fast atom beam efficiently at a relatively low discharge voltage. As is well known, atoms and molecules have a thermal motion in the atmosphere at room temperature with a kinetic energy of about 0.05 eV. "Fast atoms" are atoms and molecules that have a kinetic energy over about 0.05 eV, and when such particles are emitted in one direction, they are called "fast atom beam". Fig. 2 shows exemplarily a fast atom beam source that emits argon atoms with a kinetic energy of 0.5 to 10 keV, among conventional fast atom beam sources designed to generate fast beams of gas atoms. In the figure, reference numeral 1 denotes a cylindrical cathode that also serves as a casing, 2 a doughnut-shaped anode, 3 a DC high-voltage power supply, 4 a gas nozzle, 5 argon gas, 6 plasma, 7 fast atom beam emitting-holes, and 8 a fast atom beam. The constituent elements, exclusive of the high-voltage power supply 3, are incorporated in a vacuum container (not shown). The conventional fast atom beam source comprising the above-described constituent elements operates as follows. After the vacuum container has been sufficiently evacuated, argon gas 5 is injected into the inside of the cylindrical cathode 1 from the gas nozzle 4. Meanwhile, a high DC voltage is imposed between the anode 2 and the cathode 1 by the DC high-voltage power supply 3 in such a manner that the anode 2 has a positive potential, and the cathode 1 a negative potential. As a result of the above-described process, electric discharge occurs between the cathode 1 and the anode 2 to generate plasma 6, thus producing argon ions and electrons. During this process, electrons that are emitted from the inner wall surface at one end of the cylindrical cathode 1 are accelerated toward the anode 2 and pass through the central hole in the anode 2 to reach the inner wall surface at the other end of the cathode 1. The electrons reaching the inner wall surface at the second end lose their speed. Then, the electrons are turned around and are accelerated toward the anode 2 to pass again through the hole of the anode 2 before reaching the inner wall surface at the first end of the cathode 1. Such repeated motion of electrons forms a high-frequency vibration between the two end faces of the cylindrical cathode 1 across the anode 2, and while making the repeated motion, the electrons collide with the argon gas to produce a large number of argon ions. The argon ions produced in this way are accelerated toward each end face of the cylindrical cathode 1 to obtain a sufficiently large kinetic energy. The kinetic energy obtained at this time is, for example, about 1 keV when the discharge sustaining voltage imposed by the DC high-voltage power supply 3 is 1 kV. In other words, there is a turn point of electrons vibrating at high frequency in the vicinity of each end face of the cylindrical cathode 1. This point is a region where a large number of electrons with low energy are present. Argon ions change to argon atoms in this region by collision and recombination with the electrons. In the collision between the ions and the electrons, since the mass of the electrons are so much smaller than that of the argon ions that their mass can be ignored, the argon ions deliver the kinetic energy to the atoms exchanged of the charge without substantial loss, thus forming fast atoms. Accordingly, the kinetic energy of the fast atoms is about 1 keV. The fast atoms accelerated are emitted in the form of a fast atom beam 8 to the outside through the emitting holes 7 provided in the second end face of the cylindrical cathode 1. The above-described conventional fast atom beam source like the fast atom beam source described in D1 = Nuclear Instruments & Methods in Physics Research, Section B; Vol. B33, no. 1-4, June 1988, Amsterdam, Netherlands. Pages 867-870. "F. Shimokawa et al.: "A low-energy fast-atom source", suffers, however, from some problems described below. To increase the rate of emission of the fast atom beam, the prior art needs to raise the discharge voltage, use a magnet jointly with the described arrangement, or increase the pressure of the argon gas introduced and cannot adopt any other method, as will be inferred from the above-described matters, that does not result in an increase in the energy of the fast atom beam, or increase in the overall size of the apparatus, or an extension in the energy band of the fast atom beam, etc. Thus, the prior art involves many problems and difficulties in use. In view of the above-described circumstances, it is an object of the present invention to provide a fast atom beam source which is capable of emitting a fast atom beam efficiently at a relatively low discharge voltage and which enables a reduction in the overall size of the apparatus. To attain the above-described object, the present invention provides a fast atom beam source as set forth in claim 1. Preferred embodiments of the invention are disclosed in the dependent claims. These constituent elements, exclusive of the high voltage power supply, are incorporated in a vacuum container (not shown). The reaction gas that is introduced into the fast atom beam source casing is readily ionized on heating by mixing it with a reaction gas, for example, a halogen or a halide, thereby improving the discharge efficiency. In addition, the reaction gas is introduced into the source casing through the plate-shaped anode, and gas ions generated in the space between the two electrodes are emitted from the fast atom beam emitting-holes of the plate-shaped cathode after being accelerated by the cathode, thereby simplifying the arrangement of the apparatus, and thus enabling reduction in the overall size of the apparatus. The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiment thereof, taken in conjunction with the accompanying drawings, in which like reference numerals denote like elements, and of-which: Fig. 1 is a schematic view illustrating the arrangement of a fast atom beam source according to one embodiment of the present invention; and Fig. 2 is a schematic view illustrating the arrangement of a fast atom beam source according to a prior art. One embodiment of the present invention will be described below in detail with reference to Fig. 1. In this embodiment, constituent elements having the same functions as those of the prior art described above in connection with Fig. 2 are denoted by the same reference numerals. Referring to Fig. 1, a plate-shaped cathode 21 and a plate-shaped anode 22, which are disposed at a predetermined distance from each other, are placed in a fast atom beam source casing shown by the one-dot chain line and are connected to a DC high-voltage power supply 3 that is disposed outside the fast atom beam source casing. A hot filament 23 made of platinum is disposed in between the plate-shaped cathode 21 and the plate-shaped anode 22. The hot filament 23 is connected to a heating power supply 25 that is disposed outside the vacuum container in the same way as in the case of the DC high-voltage power supply 3. A gas nozzle 4 is secured to the plate-shaped anode 22 and communicated therewith in order to introduce a reaction gas 24 into the fast atom beam source casing from the outside thereof. The plate-shaped cathode 21 has a plurality of fast atom beam emitting-holes 7 provided in the surface thereof to enable a fast atom beam 8 to be emitted therefrom. One of the advantageous features of the present invention resides in that the reaction gas 24 contains either a halogen or a halide, which is readily ionized on heating. The operation of the fast atom beam source arranged as described above will be explained next. After a vacuum container (not shown) has been sufficiently evacuated, the reaction gas 24 is introduced into the space between the plate-shaped anode 22 and the plate-shaped cathode 21 through the gas nozzle 4. At the same time as the reaction gas 24 is introduced, the filament 23 is heated to emit thermal electrons. Further, a high DC voltage is applied between the anode 22 and the cathode 21 to induce an electric discharge between the two electrodes. As a result of the above-described process, plasma is generated, and gas ions of the reaction gas 24 and electrons are produced. The gas ions thus produced are accelerated toward the cathode 21 to give them a large energy. Furthermore, the gas ions lose their electric charges through collision with gas particles remaining in the region in the vicinity of the cathode 21 or through recombination with electrons, thereby being converted into fast atoms. The fast atoms are emitted in the form of a fast atom beam 8 to the outside from the fast atom beam emitting holes 7. In the fast atom bean source arranged and operated as described above, the reaction gas 24 is mixed with either a halogen or a halide, which are readily ionized on heating, as has already been stated. Therefore, the reaction gas 24 is ionized immediately by contact with the hot filament 23 to generate a large number of ions and electrons. Accordingly, the reaction gas 24 enables the electric discharge to be readily sustained to emit the fast atom beam 8 even if the supply voltage is relatively low. In other words, it is possible to obtain a fast atom beam with a relatively low energy. On the other hand, since the hot filament 23 is heated to a high temperature, it reacts readily with the gas 24 introduced when the latter is highly reactive, so that the hot filament 23 may deteriorate or become disconnected. To avoid such a problem, in this embodiment the hot filament 23 is made of platinum, which is an inert metal. As has been described, according to the fast atom beam source of the present invention, a gas which is readily ionized on heating is employed as a reaction gas, so that the electric discharge can be sustained at a relatively low discharge voltage and hence a fast atom beam with a relatively low energy can be obtained. In addition, since the reaction gas is introduced into the fast atom beam source casing through the anode and the resulting fast atom beam is emitted from the emitting holes provided in the cathode, it is possible to simplify the arrangement of the apparatus and reduce the overall size of the apparatus. In addition, the fast atom beam with low energy that is obtained by the present invention can fabricate the surface of a solid or modify it without causing serious damage to the solid material when collided therewith. Thus, the fast atom beam produced by the fast atom beam source of the present invention can be advantageously utilized for the fine pattern processing of semiconductors, analytical purposes, etc. In particular, since the fast atom beam is electrically neutral, it can be applied not only to metals and semiconductors but also to insulators such as plastics, ceramics, etc., to which the ion beam technique cannot effectively be applied. Although the present invention has been described through specific terms, it should be noted here that the described embodiment is not necessarily exclusive and that various changes and modifications may be imparted thereto without departing from the scope of the appended claims.

Claims: A fast atom beam source including a cathode (21) having a multiplicity of fast atom beam emitting holes (7), an anode (22) disposed at a predetermined distance from said cathode, a fast atom beam source casing, a DC high-voltage power supply connected between said cathode and said anode to induce an electric discharge between said cathode and said anode, and a gas nozzle (4) for introducing a reaction gas into said fast atom beam source casing, characterized in that said cathode (21) has a plate-shaped configuration; said anode (22) is a plate-shaped electrode disposed to face opposite to said cathode; a filament (23) is disposed in between said cathode and said anode; a power supply for heating said filament is provided; said atom beam source casing surrounds said cathode and said anode, wherein said reaction gas contains either a halogen or a halide, which is readily ionized on heating. A fast atom beam source according to Claim 1, wherein said filament is made of platinum. A fast atom beam source according to Claim 1, wherein said gas nozzle (4) is secured to said anode (22), to introduce a reaction gas to the space between said cathode (21) and said anode (22).

Inventors: HATAKEYAMA MASAHIRO, NAGAI KAZUTOSHI, HATAKEYAMA, MASAHIRO, NAGAI, KAZUTOSHI
Applicants: EBARA CORP, EBARA CORPORATION
Application year: 1992
Main classification: H05H3
IPC codes: H01J37, H05H3