Methods and Apparatus for Generating Strongly-Ionized Plasmas with Ionizational Instabilities

• US 20050184669A1
• Filed: 02/22/2004
• Published: 08/25/2005
• Est. Priority Date: 02/22/2004
• Status: Active Grant

• Current Assignee: ZOND Incorporated
• Original Assignee: ZOND Incorporated
• Inventors: Chistyakov, Roman
• Granted Patent: US 7,095,179 B2
• Time in Patent Office: Days
• US Class Current: 315/111.210
• CPC Class Codes: C23C 14/35 by application of a magnetic field, e.g. magnetron sputtering C23C14/3457 takes precedence
• CPC Class Codes: H01J 37/3266 Magnetic control means
• CPC Class Codes: H01J 37/3408 Planar magnetron sputtering
• CPC Class Codes: H01J 37/3455 Movable magnets

Abstract

Methods and apparatus for generating strongly-ionized plasmas are disclosed. A strongly-ionized plasma generator according to one embodiment includes a chamber for confining a feed gas. An anode and a cathode assembly are positioned inside the chamber. A pulsed power supply is electrically connected between the anode and the cathode assembly. The pulsed power supply generates a multi-stage voltage pulse that includes a low-power stage with a first peak voltage having a magnitude and a rise time that is sufficient to generate a weakly-ionized plasma from the feed gas. The multi-stage voltage pulse also includes a transient stage with a second peak voltage having a magnitude and a rise time that is sufficient to shift an electron energy distribution in the weakly-ionized plasma to higher energies that increase an ionization rate which results in a rapid increase in electron density and a formation of a strongly-ionized plasma.

Claims

1. A strongly-ionized plasma generator comprising:

a) a chamber for confining a feed gas;

b) an anode that is positioned inside the chamber;

c) a cathode assembly that is positioned adjacent to the anode inside the chamber; and

d) a pulsed power supply having an output that is electrically connected between the anode and the cathode assembly, the pulsed power supply generating at the output a multi-stage voltage pulse comprising;

a low-power stage including a first peak voltage having a magnitude and a rise time that is sufficient to generate a weakly-ionized plasma from the feed gas; and

a transient stage including a second peak voltage having a magnitude and a rise time that is sufficient to shift an electron energy distribution in the weakly-ionized plasma to higher energies that increase an ionization rate which results in a rapid increase in electron density and a formation of a strongly-ionized plasma.

2. The plasma generator of claim 1 further comprising a magnet that generates a magnetic field proximate to the cathode assembly.

3. The plasma generator of claim 2 wherein the magnet is movable.

4. The plasma generator of claim 2 wherein the magnetic field generated by the magnet confines the weakly-ionized and strongly ionized plasmas proximate to the cathode assembly.

5. The plasma generator of claim 2 wherein the magnetic field generated by the magnet and an electric field generated by the multi-stage voltage pulse induces an electron Hall current that raises the temperature of the electrons in the weakly-ionized plasma to a temperature that enhances the rapid increase in electron density and the formation of the strongly-ionized plasma.

6. The plasma generator of claim 1 wherein the feed gas comprises at least one of excited and metastable atoms.

7. The plasma generator of claim 1 wherein the magnitude of the first peak voltage is less than 1,000V.

8. The plasma generator of claim 1 wherein the pulsed power supply provides enough energy for the electron energy distribution in the weakly-ionized plasma to continuously shift to higher energies until the strongly ionized plasma is formed.

9. The plasma generator of claim 1 further comprising an energy storage device that is electrically coupled to the cathode assembly, the energy storage device discharging energy into the weakly-ionized plasma to enhance the rapid increase in electron density and the formation of the strongly-ionized plasma.

10. The plasma generator of claim 1 wherein the weakly-ionized plasma has a discharge current density that is less than about 0.5 A/cm² and a power density that is less than about 250 W/cm².

11. The plasma generator of claim 1 wherein the pulsed power supply generates the transient stage of the multi-stage pulse at a time that is at least 150 μ

sec after the generation of the weakly-ionized plasma.

12. The plasma generator of claim 1 wherein the rise time of the second peak voltage in the transient stage is greater than about 0.5V/μ

sec.

13. The plasma generator of claim 1 wherein the magnitude of the second peak voltage is less than about 1,000V over the first peak voltage.

14. The plasma generator of claim 1 wherein the second peak voltage in the transient stage forms ionizational instabilities in the weakly-ionized plasma.

15. The plasma generator of claim 1 wherein the transient stage generates diocotron oscillations in the weakly-ionized plasma.

16. The plasma generator of claim 1 wherein a discharge current density of the strongly-ionized plasma is greater than about 0.5 A/cm².

17. The plasma generator of claim 1 wherein the power density of the strongly-ionized plasma is greater than 250 W/cm².

18. The plasma generator of claim 1 wherein the multi-stage voltage pulse further comprises a high-power stage following the transient stage, the high-power stage having a voltage that is sufficient to sustain the strongly-ionized plasma.

19. The plasma generator of claim 18 wherein the voltage in the high-power stage comprises a relatively constant average voltage.

20. The plasma generator of claim 18 wherein a lifetime of the strongly-ionized plasma is greater than about 200 μ

sec.

21. A method of generating a strongly-ionized plasma, the method comprising:

a) supplying feed gas proximate to an anode and a cathode assembly;

b) generating a weakly-ionized plasma by applying a first voltage between the anode and the cathode assembly, the first voltage having a magnitude and a rise time that is sufficient to ignite the feed gas; and

c) generating a strongly-ionized plasma from the weakly-ionized plasma by applying a second voltage between the anode and the cathode assembly, the second voltage having a magnitude and a rise time that is sufficient to shift an electron energy distribution in the weakly-ionized plasma to higher energies that increase an ionization rate which results in a rapid increase in electron density and a formation of the strongly-ionized plasma.

22. The method of claim 21 further comprising applying a magnetic field proximate to the cathode assembly.

23. The method of claim 22 further comprising moving the magnetic field.

24. The method of claim 22 further comprising generating an electron Hall current from an electric field generated by the second voltage and from the magnetic field, the electron Hall current raising the temperature of the electrons in the weakly-ionized plasma to a temperature that enhances the increase in electron density and the form ation of the strongly-ionized plasma.

25. The method of claim 21 wherein the first and the second voltages comprise a multi-stage voltage pulse.

26. The method of claim 21 further comprising applying a third voltage between the anode and the cathode assembly that sustains the strongly-ionized plasma.

27. The method of claim 26 wherein an average value of the third voltage applied between the anode and the cathode assembly is relatively constant.

28. The method of claim 21 wherein a lifetime of the strongly-ionized plasma is greater than 200 μ

sec.

29. The method of claim 21 wherein the weakly-ionized plasma is in a steady state condition before the application of the second voltage.

30. The method of claim 21 wherein the weakly-ionized plasma is in a quasi-steady state condition before the application of the second voltage.

31. The method of claim 21 further comprising discharging energy from an energy storage device into the weakly-ionized plasma to enhance the rapid increase in electron density and the formation of a strongly-ionized plasma.

32. The method of claim 21 wherein the magnitude and the rise time of the second voltage are sufficient to generate ionizational instabilities in the weakly-ionized plasma that enhance the ionization rate resulting in a rapid increase in electron density and the formation of the strongly-ionized plasma.

33. The method of claim 32 wherein the ionizational instabilities comprise diocotron instabilities.

34. The method of claim 21 wherein the magnitude of the first voltage is less than 1,000V.

35. The method of claim 21 wherein the rise time of the second voltage applied between the anode and the cathode assembly is greater than about 0.5V/μ

sec.

36. The method of claim 21 wherein the magnitude of the second voltage is less than about 1,000V over the first voltage.

37. The method of claim 21 wherein the weakly-ionized plasma has a discharge current density that is less than about 0.5 A/cm² and a power density that is less than about 250 W/cm².

38. A method of generating a strongly-ionized plasma, the method comprising:

a) supplying feed gas proximate to an anode and a cathode assembly; and

b) applying a voltage pulse between the anode and the cathode assembly, the voltage pulse comprising;

a first peak voltage having a magnitude and a rise time that is sufficient to ignite an initial plasma from the feed gas; and

a second peak voltage having a magnitude and a rise time that is sufficient to shift an electron energy distribution in the initial plasma to higher energies that increase an ionization rate resulting in a rapid increase in electron density and a formation of the strongly-ionized plasma that is sustained for greater than 200 μ

sec.

39. The method of claim 38 further comprising applying a magnetic field proximate to the cathode assembly.

40. The method of claim 39 further comprising moving the magnetic field.

41. The method of claim 39 further comprising generating an electron Hall current from an electric field generated by the voltage pulse and from the magnetic field, the electron Hall current raising the temperature of the electrons in the initial plasma to a temperature that enhances the rapid increase in electron density and the formation of the strongly-ionized plasma.

42. The method of claim 38 wherein the voltage pulse further comprises a substantially constant voltage that sustains the strongly-ionized plasma.

43. The method of claim 38 wherein a duration of the voltage pulse is greater than 200 μ

sec.

44. The method of claim 38 wherein the magnitude of the first peak voltage is less than 1,000V.

45. The method of claim 38 wherein the magnitude of the second peak voltage is less than about 1,000V over the first peak voltage.

46. The method of claim 38 wherein the second peak voltage has a magnitude and a rise time that are sufficient to generate ionizational instabilities that enhance the ionization rate resulting in the rapid increase in electron density and the formation of the strongly-ionized plasma.

47. An apparatus for generating a strongly-ionized plasma, the apparatus comprising:

a) means for supplying feed gas proximate to an anode and a cathode assembly;

b) means for generating a weakly-ionized plasma from the feed gas;

c) means for shifting an electron energy distribution in the weakly-ionized plasma to higher energies that increase an ionization rate which results in a rapid increase in electron density and a formation of the strongly-ionized plasma from the weakly-ionized plasma; and

d) means for sustaining the strongly-ionized plasma for greater than 200 μ

sec.