Coating apparatus – Gas or vapor deposition – With treating means
Patent
1996-05-23
1997-06-10
Niebling, John
Coating apparatus
Gas or vapor deposition
With treating means
118723MW, 427575, C23C 1600
Patent
active
056371500
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a device and a method for forming a plasma by application of microwaves.
It is known that, in order to create a plasma, a volume of gas can be subjected to high-frequency excitation by an alternating electrical field, possibly in combination with a static magnetic field.
This superimposition of an alternating electrical field on a static magnetic field causes a cyclotron electron resonance effect, providing optimal conditions for gas ionization.
In practice, a plasma is created from a gas volume by placing the gas volume in a high-frequency alternating electrical field generated by a metal antenna on which a static magnetic field may be superimposed.
SUMMARY OF THE INVENTION
The goal of the invention is to provide a new device for forming a plasma that which is large in dimension and of any shape, particularly one with a rectangular or circular cross section.
The present invention relates to a device for forming a plasma from microwaves, comprising an ionization chamber into which a gas can be introduced to undergo excitation due to the presence of a high-frequency alternating electrical field emitted by a plurality of metal antennas, characterized in that it includes a gas-free volume wherein said metal antennas are disposed parallel to each other, distributed at the nodes of a regular plane network, one end of each antenna extending outside said gas-free volume in the ionization chamber, with an induction loop emitting microwaves in the gas-free volume.
According to the invention, only the ends of the antennas are immersed in the microwave plasma from which the ion beam is extracted.
The advantage of this device is that the plasma, which occupies a small volume by comparison to the total volume, has little effect on the excitation conditions of the latter.
In addition, the microwave energy is supplied through an induction loops to the periodic structure at a single point in the volume containing the antennas.
According to the invention, "induction loop" is understood to be any means that can supply the microwave energy to the periodic structure. In particular, it is an associated antenna.
With this principle, highly varied devices can be built depending on the positions of the antennas distributed in two dimensions; however their length is, according to the invention, approximately an odd multiple of half the wavelength of the microwave in vacuum.
The emissive surface of the plasma, and hence the shape of the extracted-ion beam cross section, may be chosen for application to numerous industrial applications, particularly surface treatment by ion beams.
In one particular embodiment of the invention, the device also has means for generating a polarization electrical field in the gas-free volume, which field is able to concentrate the ions formed in the vicinity of the array of metal antennas.
Advantageously, the means for generating the polarization electrical field include the array of metal antennas serving for application of microwaves in the plasma.
The present invention also relates to a process for forming a plasma from microwaves in a device as described above, characterized in that there is added, to the excitation electrical field, another quasi-static polarization electrical field which tends to concentrate the ions around each of the microwave-emitting antennas. In plasma theory, this concentration of ions is designated "ion sheath."
In other words, the method according to the invention consists of adding, to the electrical and magnetic excitation fields, another and quasi-static polarization electrical field which forms an ion sheath around the array of microwave-emitting antennas.
This ion sheath behaves like an electrical capacitance that offsets the self-inductive component of the antenna, which self-inductive component appears naturally when the plasma is subjected to the microwaves, principally under the conditions of cyclotron electron resonance.
In one embodiment of the invention, the polarization field is emitted by the ar
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Pichot et al. "Microwave multipolar plasmas excited by distributed electron cyclotron resonance: Concept and performance." Review of Scientific Instruments, vol. 59, No. 7, Jul. 1988, pp. 1072-1075.
Ngo Phong Linh et al. "Excitation of the Half-Frequency of the Input Signal in the Response of an Antenna." IEEE Transactions on Plasma Science, vol. 18, No. 4, Aug. 1990, pp. 717-724.
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Aubert Jean
Wartski Louis
Chang Joni Y.
Niebling John
Plasmion
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