Methods and apparatus for generating high-density plasma

• US 20040085023A1
• Filed: 11/04/2002
• Published: 05/06/2004
• Est. Priority Date: 11/04/2002
• Status: Active Grant

• Current Assignee: ZOND Incorporated
• Original Assignee: ZOND Incorporated
• Inventors: Chistyakov, Roman
• Granted Patent: US 6,853,142 B2
• Time in Patent Office: Days
• US Class Current: 315/111.21
• CPC Class Codes: C23C 14/3471 Introduction of auxiliary energy into the plasma
• CPC Class Codes: C23C 14/354 Introduction of auxiliary energy into the plasma
• CPC Class Codes: H01J 37/32321 Discharge generated by other radiation H01J37/32055, H01J37/32073, H01J37/32082, H01J37/32192, H01J37/32348 take precedence
• CPC Class Codes: H01J 37/34 operating with cathodic sputtering H01J37/36 takes precedence ; methods of cathodic sputtering C23C14/34

Abstract

Methods and apparatus for generating a strongly-ionized plasma are described. An apparatus for generating a strongly-ionized plasma according to the present invention includes an anode and a cathode that is positioned adjacent to the anode to form a gap there between. An ionization source generates a weakly-ionized plasma proximate to the cathode. A power supply produces an electric field in the gap between the anode and the cathode. The electric field generates excited atoms in the weakly-ionized plasma and generates secondary electrons from the cathode. The secondary electrons ionize the excited atoms, thereby creating the strongly-ionized plasma.

Claims

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

an ionization source that generates a weakly-ionized plasma from a volume of feed gas;

a power supply that applies an electrical pulse across the weakly-ionized plasma to generate the strongly-ionized plasma; and

a means for exchanging the strongly-ionized plasma with a second volume of feed gas while applying the electrical pulse across the second volume of feed gas to generate an additional strongly-ionized plasma.

2. The apparatus of claim 1 wherein the power supply applies the electrical pulse across the weakly-ionized plasma to excite atoms in the weakly-ionized plasma and to generate secondary electrons, the secondary electrons ionizing the excited atoms, thereby creating the strongly-ionized plasma.

3. The apparatus of claim 1 further comprising a gas exchange means for exchanging the weakly-ionized plasma with a third volume of feed gas while applying the electrical pulse across the third volume of feed gas.

4. The apparatus of claim 1 wherein the power supply generates a constant power.

5. The apparatus of claim 1 wherein the power supply generates a constant voltage.

6. The apparatus of claim 1 wherein the ionization source is chosen from the group comprising an electrode coupled to a DC power supply, an electrode coupled to an AC power supply, a UV source, an X-ray source, an electron beam source, an ion beam source, an inductively coupled plasma source, a capacitively coupled plasma source, and a microwave plasma source.

7. The apparatus of claim 1 further comprising a magnet that is positioned to generate a magnetic field proximate to the weakly-ionized plasma, the magnetic field trapping electrons in the weakly-ionized plasma.

8. The apparatus of claim 7 wherein the magnet comprises an electromagnet.

9. The apparatus of claim 7 wherein the magnet is movable.

10. A method for generating a strongly-ionized plasma, the method comprising:

ionizing a volume of feed gas to form a weakly-ionized plasma;

applying an electrical pulse across the weakly-ionized plasma to generate the strongly-ionized plasma; and

exchanging the strongly-ionized plasma with a second volume of feed gas while applying the electrical pulse across the second volume of feed gas to generate an additional strongly-ionized plasma.

11. The method of claim 10 wherein the applying the electrical pulse across the weakly-ionized plasma excites atoms in the weakly-ionized plasma and generates secondary electrons, the secondary electrons ionizing the excited atoms, thereby creating a strongly-ionized plasma.

12. The method of claim 10 further comprising exchanging the weakly-ionized plasma with a third volume of feed gas while applying the electrical pulse across the third volume of feed gas.

13. The method of claim 10 wherein the applying the. electrical pulse comprises applying a quasi-static electric field across the weakly-ionized plasma.

14. The method of claim 10 further comprising selecting at least one of a pulse amplitude and a pulse width of the electrical pulse in order to increase an ionization rate of the strongly-ionized plasma.

15. The method of claim 10 further comprising selecting at least one of a pulse amplitude and a pulse width of the electrical pulse in order to cause the strongly-ionized plasma to be substantially uniform.

16. The method of claim 10 wherein the electrical pulse comprises a rise time that is between about 0.1 microsecond and 10 seconds.

17. The method of claim 10 wherein the peak plasma density of the weakly-ionized plasma is less than about 10 cm

18. The method of claim 10 wherein the peak plasma density of the strongly-ionized plasma is greater than about 10¹² cm⁻

3.

19. The method of claim 10 wherein the ionizing the feed gas comprises exposing the feed gas to one of a static electric field, an pulsed electric field, UV radiation, X-ray radiation, electron beam radiation, and an ion beam.

20. The method of claim 10 further comprising generating a magnetic field proximate to the weakly-ionized plasma, the magnetic field trapping electrons in the weakly-ionized plasma.

21. The method of claim 10 wherein the weakly-ionized plasma reduces the probability of developing an electrical breakdown condition.

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

an anode;

a cathode that is positioned adjacent to the anode and forming a gap there between;

an ionization source that generates a weakly-ionized plasma proximate to the cathode; and

a power supply that produces an electric field across the gap, the electric field generating excited atoms in the weakly-ionized plasma and generating secondary electrons from the cathode, the secondary electrons ionizing the excited atoms, thereby creating the strongly-ionized plasma.

23. The apparatus of claim 22 wherein the power supply generates a constant power.

24. The apparatus of claim 22 wherein the power supply generates a constant voltage.

25. The apparatus of claim 22 wherein the electric field comprises a quasi-static electric field.

26. The apparatus of claim 22 wherein the electric field comprises a pulsed electric field.

27. The apparatus of claim 22 wherein a rise time of the electric field is chosen to increase an ionization rate of the excited atoms in the weakly-ionized plasma.

28. The apparatus of claim 22 wherein the weakly-ionized plasma reduces the probability of developing an electrical breakdown condition between the anode and the cathode.

29. The apparatus of claim 22 wherein the strongly-ionized plasma is substantially uniform proximate to the cathode.

30. The apparatus of claim 22 wherein a dimension of the gap between the anode and the cathode is chosen to increase an ionization rate of the excited atoms in the weakly-ionized plasma.

31. The apparatus of claim 22 wherein the ionization source is chosen from the group comprising an electrode coupled to a DC power supply, an electrode coupled to an AC power supply, a UV source, an X-ray source, an electron beam source, an ion beam source, an inductively coupled plasma source, a capacitively coupled plasma source, and a microwave plasma source.

32. The apparatus of claim 22 further comprising a magnet that is positioned to generate a magnetic field proximate to the weakly-ionized plasma, the magnetic field trapping electrons in the weakly-ionized plasma proximate to the cathode.

33. A method for generating a strongly-ionized plasma, the method comprising:

ionizing a feed gas to generate a weakly-ionized plasma proximate to a cathode; and

applying an electric field across the weakly-ionized plasma in order to excite atoms in the weakly-ionized plasma and to generate secondary electrons from the cathode, the secondary electrons ionizing the excited atoms, thereby creating the strongly-ionized plasma.

34. The method of claim 33 wherein the applying the electric field comprises applying a quasi-static electric field.

35. The method of claim 33 wherein the applying an electric field comprises applying the electric field at a constant power.

36. The method of claim 33 wherein the applying an electric field comprises applying the electric field at a constant voltage.

37. The method of claim 33 wherein the applying the electric field comprises applying an electrical pulse across the weakly-ionized plasma.

38. The method of claim 37 further comprising selecting at least one of a pulse amplitude and a pulse width of the electrical pulse in order to increase an ionization rate of the strongly-ionized plasma.

39. The method of claim 37 further comprising selecting at least one of a pulse amplitude and a pulse width of the electrical pulse in order to cause the strongly-ionized plasma to be substantially uniform in an area adjacent to a surface of the cathode.

40. The method of claim 33 wherein the strongly-ionized plasma is substantially uniform proximate to the cathode.

41. The method of claim 33 further comprising generating a magnetic field proximate to the weakly-ionized plasma, the magnetic field trapping electrons in the weakly-ionized plasma.

42. The method of claim 33 wherein the weakly-ionized plasma reduces the probability of developing an electrical breakdown condition between the anode and the cathode.

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

means for ionizing a volume of feed gas to form a weakly-ionized plasma;

means for applying an electrical pulse across the weakly-ionized plasma to generate the strongly-ionized plasma; and

means for exchanging the strongly-ionized plasma with a second volume of feed gas while applying the electrical pulse across the second volume of feed gas to generate an additional strongly-ionized plasma.

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

means for ionizing a feed gas to generate a weakly-ionized plasma proximate to a cathode; and

means for applying an electric field across the weakly-ionized plasma in order to excite atoms in the weakly-ionized plasma and to generate secondary electrons from the cathode, the secondary electrons ionizing the excited atoms, thereby creating the strongly-ionized plasma.