US 4,507,588 AGranted

Ion generating apparatus and method for the use thereof

AssigneeBoard of Trustees operating Michigan State University

InventorsJes Asmussen, Joseph J. Root

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Abstract

A radio frequency wave ion generating apparatus which provides a thin disc shaped plasma adjacent an ion attracting means is described. The radio frequency waves are preferably microwaves. Several improvements to microwave plasma generation are described including the steps of generation of a resonantly sustained microwave discharge inside a microwave/plasma coupler or cavity (11) to ignite the plasma; probe (14) and length tuning of the microwave/plasma coupler by means of a sliding short (12) during operation of the plasma and minimization of the plasma volume inside the coupler in a chamber (15) to produce the disc plasma. The apparatus is particularly useful for internal ion or free radical irradiation of various materials provided in the plasma or for ion acceleration outside the cavity for use as an ion engine or as an ion source for irradiation of the materials.

Claims18

Dependent claims

In an ion generating apparatus including a plasma source employing a radio frequency wave coupler which is excited in one or more of its TE or TM modes of resonance to produce the plasma in the coupler and optionally including a static magnetic field which aids in confining the ions in the coupler including a probe inside the coupler which couples the radio frequency waves to the coupler and including ion attracting means for attracting the ions from said plasma preferably by means of a suitable voltage potential which accelerates the ions, the improvement which comprises:

(a) an electrically insulated plasma defining chamber (15) having a central longitudinal axis and mounted in closely spaced relationship to an area (16) of a metallic radio frequency wave coupler which is in the shape of a hollow cavity (11);
(b) at least one metallic ion attracting means (17a) mounted adjacent to and electrically insulated from the insulated chamber which ion attracting means forms part of the radio frequency coupler;
(c) gas supply means (18, 19) for providing a gas which is ionized to form the plasma in the plasma defining chamber, wherein the radio frequency wave applied to the coupler creates and then maintains the plasma in the shape of an elongate, thin disk adjacent to the ion attracting means and perpendicular and surrounding to the axis in the chamber during steady state operation of the apparatus;
and
(d) movable metal plate means (12) in the cavity mounted perpendicular to the axis and movable towards and away from the plasma disk;
and
(e) a movable probe (14) connected to and extending inside the coupler for coupling the radio frequency waves to the coupler wherein movement of the plate means and the probe in the coupler achieves a selected TE or TM mode of resonance of the radio frequency wave in the coupler and varies the resonance of the mode.

4 more elements

In an ion source apparatus including a plasma source employing a microwave cavity (11) as a coupler which is excited in one or more of its TE or TM modes of resonance including a probe inside the cavity which couples radio frequency waves to the cavity and optionally including a static magnetic field which aids in confining the ions in the coupler and including electrostatic accelerating means (17a) adjacent an opening from the cavity for extracting the ions from said plasma by means of a suitable voltage potential which accelerates the ions from the cavity in an ion stream, wherein the plasma, the opening and ion accelerating means are maintained at a reduced pressure in operation, the improvement which comprises:

(a) an electrically insulated chamber (15) having a central longitudinal axis in closely spaced relationship to the opening in a hollow metal cavity (11);
(b) at least one electrically insulated metallic grid means (17a) mounted over the opening and adjacent to and outside the insulated chamber as the electrostatic accelerating means for the ions and which forms part of the microwave cavity;
(c) gas supply means (18, 19) for providing a gas which is ionized to form the plasma in the insulated chamber, wherein the microwave resonance applied to the cavity and plasma creates and then maintains the plasma in the shape of a disk in the opening adjacent to the grid means and perpendicular and surrounding the axis in the chamber;
and
(d) movable metal plate means (12) in the cavity mounted perpendicular to the axis and movable towards and away from the opening;
and
(e) a movable probe (14) connected to and extending inside the cavity for coupling the radio frequency waves to the cavity, wherein upon movement of the plate means and the probe in the cavity achieves selected TE or TM mode of resonance of the microwave in the cavity and varies the resonance of the mode.

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The method which comprises:

(a) providing an ion generating apparatus including a plasma source employing a radio frequency wave coupler which is excited in one or more of its TE or TM modes of resonance to produce the plasma in the coupler and optionally including a static magnetic field which aids in confining the ions in the coupler including a probe inside the coupler which couples the radio frequency waves to the coupler and including ion attracting means (17b) for attracting the ions from said plasma by means of a suitable voltage potential which accelerates the ions, wherein the plasma, and ion attracting means are maintained at a reduced pressure in operation wherein the ion source apparatus includes the improvements of:
(1) an electrically insulated chamber (15) having a longitudinal axis and mounted in closely spaced relationship to an area (16) of a metallic radio frequency wave coupler which is in the shape of a hollow cavity;
(2) at least one ion attracting means 17a mounted adjacent to and insulated from the insulated chamber which ion attracting means forms part of the radio frequency wave coupler;
(3) gas supply means (18, 19) for providing a gas which is ionized to form the plasma in the insulated chamber;
(4) movable metal plate means (12) in the cavity mounted perpendicular to the axis and movable towards and away from the plasma disk;
and
(5) a movable probe (14) connected to and extending inside the coupler for coupling the radio frequency waves to the coupler;
(b) forming the plasma in the chamber with the radio frequency wave at an elevated gas pressure below atmospheric pressure and at elevated gas flow rates from the gas supply means;
(c) reducing the gas pressure and flow rate of the gas into the chamber to provide a plasma disk adjacent the ion attracting means, wherein the radio frequency wave resonance applied to the coupler creates and then maintains the plasma in the shape of an elongate, thin disk adjacent to the ion attracting means and perpendicular and surrounding to the axis in the chamber during steady state operation of the apparatus;
(d) tuning the coupler using the movable plate means by movement towards and away from the plasma disk and by movement of the probe into and out of the coupler, wherein the movement of the plate means and probe in the cavity achieves a selected TE or TM mode of resonance of the cavity and varies the resonance of the mode;
and
(e) attracting the ions from the plasma with the ion attracting means.

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Dependencies are inferred from the claim text.