RF system, magnetic filter, and high voltage isolation for an inductively coupled plasma ion source

• US 9,655,223 B2
• Filed: 09/16/2013
• Issued: 05/16/2017
• Est. Priority Date: 09/14/2012
• Status: Active Grant

• Current Assignee: Oregon Physics LLC
• Original Assignee: Oregon Physics LLC
• Inventors: Tesch, Paul P., Boswell, Roderick W., Smith, Noel S., Martin, Noel P.
• Primary Examiner(s): Owens, Douglas W
• Assistant Examiner(s): Sathiraju, Srinivas
• Application Number:
  US14/028,305
• Publication Number:
  US 20140077699A1
• Time in Patent Office: 1,338 Days
• Field of Search: None
• CPC Class Codes: H01J 27/16 using high-frequency excitation, e.g. microwave excitation
• CPC Class Codes: H01J 37/08 Ion sources; Ion guns
• CPC Class Codes: H01J 37/32082 Radio frequency generated discharge H01J37/32357, H01J37/32366, H01J37/32394 and H01J37/32403 take precedence
• CPC Class Codes: H01J 49/105 using high-frequency excitation, e.g. microwave excitation, Inductively Coupled Plasma [ICP]
• CPC Class Codes: H01J 49/142 using a solid target which is not previously vapourised
• CPC Class Codes: H05H 1/46 using applied electromagnetic fields, e.g. high frequency or microwave energy H05H1/26 takes precedence
• CPC Class Codes: H05H 1/4652 using inductive coupling means, e.g. coils

Abstract

In a plasma ion source having an induction coil adjacent to a reactor chamber for inductively coupling power into the plasma from a radio frequency power source and designed for negative and positive ion extraction, a method for operating the source according to the invention comprises providing radio frequency power to the induction coil with a RF amplifier operating with a variable frequency connected to a matching network mainly comprised of fixed value capacitors. In this device the impedance between the RF power source and the plasma ion source is matched by tuning the RF frequency rather than adjusting the capacitance of the matching network. An option to use a RF power source utilizing lateral diffused metal oxide semiconductor field effect transistor based amplifiers is disclosed.

Claims

1. A plasma source for processing or imaging a substrate, secondary ion mass spectrometry, ion source for proton therapy, ion thrusters, and high energy particle accelerators comprising:

a reactor chamber within which a plasma is generated to produce at least one plasma product for processing or imaging the substrate, ion source for proton therapy, ion thrusters, and high energy particle accelerators, the reactor chamber including outer walls that are actively biased to a high voltage;

a gas source coupled to the reactor chamber to provide gas into the reaction chamber;

an exit aperture coupled to the reactor chamber to allow extraction of ions from the reactor chamber;

and a magnetic circuit comprising a source of magnetic flux that is electrically isolated from the reactor chamber and located at ground potential, and a high permeability magnetic circuit formed of magnetic permeability material in physical contact with the reactor chamber and located adjacent the reactor chamber exit aperture, with said magnetic circuit configured to produce a transverse DC magnetic field adjacent the exit aperture of the reactor chamber and channel magnetic flux through a high voltage gap to provide magnetic flux into the reactor chamber, with one portion of the circuit containing a high magnetic permeability material, the one portion being biased to high voltage and electrically isolated from another portion of the magnetic circuit by a dielectric fluid.

2. The plasma source of claim 1, wherein an electromagnetic source of magnetic flux is in contact with a dielectric fluid and thermally cooled by the dielectric fluid.

3. The plasma source of claim 1, further including a second portion of the magnetic circuit containing a high magnetic permeable material near or at ground potential that couples magnetic flux into the portion of the magnetic circuit biased to high voltage.

4. The plasma source of claim 1, where a nonmagnetic tube is connected to the reactor chamber and magnetic flux is transferred through the nonmagnetic tube.

5. A plasma source for processing or imaging a substrate, ion source for proton therapy, secondary ion mass spectrometry, ion thrusters, and high energy particle accelerators comprising:

a reactor chamber within which a plasma is generated to produce at least one plasma product for processing or imaging the substrate, secondary ion mass spectrometry, ion source for proton therapy, ion thrusters, and high energy particle accelerators, the reactor chamber including outer walls that are actively biased to a high voltage;

a gas source coupled to the reactor chamber to provide gas into the reaction chamber;

an exit aperture biased to high voltage coupled to the reactor chamber to allow extraction of ions from the reactor chamber;

a transverse magnetic field applied at the exit aperture via a magnetic circuit configured with outer magnetic poles biased at ground potential formed outside a lateral expanse of the reactor chamber and inner magnetic poles biased at the reactor chamber voltage and located within the lateral expanse of the reactor chamber;

a first source of radio frequency power; and

a plurality of induction coils adjacent to the reactor chamber and coupled to said first source of radio frequency power to inductively couple power into the plasma from said first source of radio frequency power.

11. The plasma source of claim 5, said magnetic circuit being further configured to channel magnetic flux through a high voltage gap adjacent said exit aperture.

6. A plasma source for processing or imaging a substrate, ion source for proton therapy, ion thrusters, and high energy particle accelerators comprising:

a reactor chamber within which a plasma is generated to produce at least one plasma product for processing or imaging the substrate, secondary ion mass spectrometry, ion source for proton therapy, ion thrusters, and high energy particle accelerators, the reactor chamber including outer walls that are actively biased to a high voltage;

a gas source coupled to the reactor chamber to provide gas into the reaction chamber;

an exit aperture coupled to the reactor chamber to allow extraction of ions from the reactor chamber; and

an insulator made up of a capillary or tube with an inner diameter much smaller than its length, where the insulator has a spiral, serpentine, or coiled path to reduce the electric field along the tube or capillary length.

7. The plasma source of claim 6, wherein a second small capillary or aperture restricts the flow of gas to produce a pressure in the plasma chamber that is significantly lower than the pressure from the gas source.

8. The plasma source of claim 7, wherein the second capillary or aperture is maintained at constant voltage.

9. The plasma source of claim 6, wherein the pressure in the plasma tube is 1-100 millitorr.

10. The plasma source of claim 6, wherein the insulator is immersed in a dielectric fluid.