Inductively-coupled toroidal plasma source

• US 6,815,633 B1
• Filed: 03/12/2001
• Issued: 11/09/2004
• Est. Priority Date: 06/26/1997
• Status: Expired due to Term

• Current Assignee: MKS Instruments Incorporated
• Original Assignee: Applied Science & Technology, Inc. (MKS Instruments Incorporated)
• Inventors: Chen, Xing, Holber, William M., Cowe, Andrew Barnett, Bystyak, Ilya M., Georgelis, Eric, Bortkiewicz, Andrzej
• Primary Examiner(s): PASCHALL, MARK H
• Application Number:
  US09/804,650
• Time in Patent Office: 1,338 Days
• Field of Search: 219/121.36, 219/121.37, 219/121.48, 219/121.52, 219/121.59, 219/121.54, 219/121.57, 219/74, 219/75, 219/121.43, 219/121.4, 219/121.41, 315/111.51, 156/345.38, 156/345.48, 204/298.31
• US Class Current: 219/121.54
• CPC Class Codes: H01J 27/16 using high-frequency excitation, e.g. microwave excitation
• CPC Class Codes: H01J 37/32009 Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources plasma generation in general H05H1/24
• CPC Class Codes: H01J 37/321 the radio frequency energy being inductively coupled to the plasma
• CPC Class Codes: H01J 37/32357 Generation remote from the workpiece, e.g. down-stream
• CPC Class Codes: H01J 37/32862 In situ cleaning of vessels and/or internal parts

Abstract

Apparatus for dissociating gases includes a plasma chamber comprising a gas. A first transformer having a first magnetic core surrounds a first portion of the plasma chamber and has a first primary winding. A second transformer having a second magnetic core surrounds a second portion of the plasma chamber and has a second primary winding. A first solid state AC switching power supply including one or more switching semiconductor devices is coupled to a first voltage supply and has a first output that is coupled to the first primary winding. A second solid state AC switching power supply including one or more switching semiconductor devices is coupled to a second voltage supply and has a second output that is coupled to the second primary winding. The first solid state AC switching power supply drives a first AC current in the first primary winding. The second solid state AC switching power supply drives a second AC current in the second primary winding. The first AC current and the second AC current induce a combined AC potential inside the plasma chamber that directly forms a toroidal plasma that completes a secondary circuit of the transformer and that dissociates the gas.

Claims

1. An apparatus for dissociating gases, the apparatus comprising:

a. a plasma chamber comprising a gas;

b. a first transformer having a first magnetic core surrounding a first portion of the plasma chamber and having a first primary winding, and a second transformer having a second magnetic core surrounding a second portion of the plasma chamber and having a second primary winding; and

c. a first solid state AC switching power supply comprising one or more switching semiconductor devices that are coupled to a first voltage supply and having a first output that is coupled to the first primary winding, and a second solid state AC switching power supply comprising one or more switching semiconductor devices that are coupled to a second voltage supply and having a second output that is coupled to the second primary winding,

the first solid state AC switching power supply driving a first AC current in the first primary winding, and the second solid state AC switching power supply driving a second AC current in the second primary winding, the first AC current and the second AC current inducing a combined AC potential inside the plasma chamber that directly forms a toroidal plasma that completes a secondary circuit of the transformer and that dissociates the gas.

2. The apparatus of claim 1 wherein the one or more switching semiconductor devices comprises one or more switching transistors.

3. The apparatus of claim 1 wherein the output of the one or more switching semiconductor devices is directly coupled to the primary winding.

4. The apparatus of claim 1 wherein the plasma chamber comprises an electrically conductive material and at least one dielectric region that forms an electrical discontinuity in the conductive material.

5. The apparatus of claim 4 wherein the electrically conductive material comprises aluminum.

6. The apparatus of claim 5 wherein the aluminum is anodized.

7. The apparatus of claim 4 wherein the plasma chamber comprising the electrically conductive material is segmented with at least two dielectric gaps, the at least two dielectric gaps reducing the potential difference between the plasma and the metal plasma chamber, thereby distributing a plasma loop voltage across the at least two dielectric gaps.

8. The apparatus of claim 4 further comprising a voltage divider circuit that is electrically coupled across the at least two dielectric gaps.

9. The apparatus of claim 1 wherein the plasma chamber comprises a dielectric material.

10. The apparatus of claim 9 wherein the dielectric material comprises quartz.

11. The apparatus of claim 9 wherein the plasma chamber comprising the dielectric material is thermally bonded to a metal supporting structure.

12. The apparatus of claim 11 wherein the metal supporting structure comprises cooling channels that transport cooling fluid, the cooling fluid controlling the temperature of the plasma chamber.

13. The apparatus of claim 1 wherein the first and the second solid state AC switching power supply are substantially identical.

14. The apparatus of claim 1 wherein the first and the second solid state AC switching power supply comprise a single power supply unit.

15. The apparatus of claim 1 wherein the first and the second voltage supply comprise a voltage regulator circuit, the first and the second voltage regulating circuit regulating a voltage generated by the first and the second voltage supply, respectively.

16. The apparatus of claim 1 wherein the plasma chamber comprises a portion of an outer surface of a process chamber.

17. The apparatus of claim 16 wherein the plasma extends into the process chamber.

18. The apparatus of claim 16 wherein a portion of the first and the second magnetic core are positioned within the process chamber.

19. The apparatus of claim 1 further comprising an electrode positioned in the plasma chamber, the electrode generating free charges that assist the ignition of the plasma in the plasma chamber.

20. The apparatus of claim 1 further comprising a secondary winding that resonates with the primary winding, the secondary winding raising the voltage in the plasma chamber to assist ignition of the plasma in the plasma chamber.

21. The apparatus of claim 1 further comprising an ultraviolet light source that is optically coupled to the plasma chamber, the ultraviolet light source generating free changes that assist the ignition of the plasma in the plasma chamber.

22. The apparatus of claim 1 further comprising a circuit for measuring electrical parameters associated with at least one of the first and the second primary winding and the plasma, the electrical parameters including at least one of a current driving the primary winding, a voltage across the primary winding, an average power in the primary winding, and a peak power in the primary winding.

23. The apparatus of claim 22 further comprising a power control circuit having an input coupled to an output of the circuit for measuring electrical parameters associated with the at least one of the first and the second primary winding and the plasma and having an output coupled to a control input of the first and the second solid state AC switching power supply, the power control circuit controlling voltage and current supplied to the primary winding.

24. A method for dissociating gases, the method comprising:

a. confining a gas in a plasma chamber at a pressure;

b. generating a first and a second current with a first and a second solid state AC switching power supply, respectively; and

c. inducing a combined AC potential inside the plasma chamber by passing the first current though a first primary winding having a first magnetic core surrounding a first portion of the plasma chamber, and by passing the second current though a second primary winding having a second magnetic core surrounding a second portion of the plasma chamber, the combined induced AC potential directly forming a toroidal plasma that completes a secondary circuit of the transformer and dissociates the gas.

25. The method of claim 24 further comprising regulating the current generated with the first and the second solid state AC switching power supply.

26. The method of claim 24 further comprising providing an initial ionization event in the plasma chamber.

27. The method of claim 26 wherein the providing an initial ionization event in the plasma chamber comprises applying a voltage pulse to at least one of the first and the second primary winding.

28. The method of claim 26 wherein the providing an initial ionization event in the plasma chamber comprises exposing an inside of the plasma chamber to ultraviolet light.

29. The method of claim 24 wherein the gas comprises at least one of a noble gas and a reactive gas.

30. The method of claim 24 further comprising measuring electrical parameters including at least one of the current passing though the first and the second primary winding, a voltage across the first and the second primary winding, an average power in the first and the second primary winding, and a peak power in the first and the second primary winding.

31. The method of claim 30 further comprising the step of adjusting a magnitude of the current generated by the first and the second solid state AC switching power supply in response to the measured electrical parameters.

32. The method of claim 24 wherein the pressure is substantially between 1 mtorr and 100 torr.

33. The method of claim 24 wherein an electric field of the plasma is substantially between 1-100 V/cm.

34. A method for cleaning a process chamber, the method comprising:

a. confining a gas in a plasma chamber comprising a portion of the outer surface of the process chamber;

b. generating a first and a second current with a first and a second solid state AC switching power supply, respectively;

c. inducing a combined AC potential inside the plasma chamber by passing the first current though a first primary winding having a first magnetic core surrounding a first portion of the plasma chamber, and by passing the second current though a second primary winding having a second magnetic core surrounding a second portion of the plasma chamber, the combined induced AC potential directly forming a toroidal plasma that completes a secondary circuit of the transformer and dissociates the gas; and

d. directing the dissociated gas into the process chamber, thereby cleaning the process chamber.

35. The method of claim 34 wherein the reactive gas comprises at least one of an oxygen and a fluorine containing gas.

36. A method for reducing surface erosion in a reactive gas source, the method comprising:

confining a gas in a plasma chamber comprising an electrically conductive material segmented into portions by multiple dielectric regions;

providing one or more transformers each having a magnetic core surrounding a respective portion of the plasma chamber and having a primary winding;

inducing an AC potential inside the plasma chamber by supplying an AC current generated by a solid state AC switching power supply, without requiring the use of an impedance matching network, to the primary winding of the one or more transformers, the induced AC potential forming a toroidal plasma inside the plasma chamber that completes a secondary circuit of the one or more transformers and dissociates the gas; and

distributing a plasma loop voltage across multiple dielectric regions to reduce surface erosion in the plasma chamber.

37. The method of claim 36 further comprising distributing the plasma loop voltage equally across each of the multiple dielectric regions.

38. The method of claim 36 further comprising reducing the plasma loop voltage to about 100 volts or lower across each of the multiple dielectric regions.

39. The method of claim 36 further comprising passing a fluid through cooling channels thermally bonded to the plasma chamber to control the temperature of the plasma chamber.

40. The method of claim 36 wherein the AC switching power supply supplies the AC current to the primary winding without using the impedance matching network.

41. The method of claim 36 wherein the AC switching power supply supplies the AC current to the primary winding without using a conventional impedance matching network.

42. The method of claim 36 wherein the AC switching power supply comprises one or more switching transistors that supply the AC current to the primary winding without requiring the use of the conventional impedance matching network.

43. The method of claim 36 further comprising protecting the dielectric region from the plasma by a protrusion in the plasma chamber.

44. The method of claim 36 further comprising using a voltage divider circuit to control the distribution of the plasma loop voltage across multiple dielectric regions.

45. A method for reducing surface erosion in a reactive gas source, the method comprising:

confining a gas in a plasma chamber segmented into portions by multiple dielectric regions;

providing a transformer having a magnetic core surrounding a portion of the plasma chamber and having a primary winding;

inducing an AC potential inside the plasma chamber, by supplying an AC current generated by a solid state AC switching power supply to the primary winding of the transformer, that forms a toroidal plasma inside the plasma chamber that completes a secondary circuit of the transformer and dissociates the gas; and

distributing a plasma loop voltage across multiple dielectric regions to reduce surface erosion in the plasma chamber.

46. The method of claim 45 further comprising distributing the plasma loop voltage equally across each of the multiple dielectric regions.

47. The method of claim 45 further comprising forming the plasma chamber using at least one of a metallic material and a coated metallic material.

48. A method for reducing surface erosion in a reactive gas source, the method comprising:

confining a gas in a plasma chamber segmented into portions by multiple dielectric regions;

providing a plurality of transformers each having a magnetic core surrounding a respective portion of the plasma chamber and having a primary winding;

inducing a combined AC potential inside the plasma chamber, by supplying an AC current generated by a solid state AC switching power supply to the primary windings of the transformers, the combined induced AC potential forming a toroidal plasma inside the plasma chamber that completes a secondary circuit of the transformer and dissociates the gas; and

distributing a plasma loop voltage across multiple dielectric regions to reduce surface erosion in the plasma chamber.

49. The method of claim 48 wherein the AC switching power supply supplies the AC current to the primary windings without requiring the use of an impedance matching network.

50. The method of claim 49 wherein the AC switching power supply supplies the AC current to the primary windings without using an impedance matching network.

51. The method of claim 50 wherein the AC switching power supply supplies the AC current to the primary windings without using a conventional impedance matching network.

52. The method of claim 48 further comprising distributing the plasma loop voltage equally across each of the multiple dielectric regions.

53. The method of claim 48 further comprising reducing the plasma loop voltage to about 100 volts or lower across each of the multiple dielectric regions.

54. A reactive gas source for dissociating gases in a toroidal plasma comprising:

a plasma chamber comprising multiple dielectric regions that segment the plasma chamber into portions;

one or more transformers each having a magnetic core surrounding a respective portion of the plasma chamber and a primary winding;

a gas inlet for providing a feed gas to the plasma chamber; and

a solid state AC switching power supply comprising one or more switching transistors and supplying an AC current to the primary windings of the one or more transformers without requiring the use of an impedance matching network, the AC current in the primary windings inducing a combined AC potential inside the plasma chamber to form the toroidal plasma that completes a secondary circuit of the transformer and dissociates the feed gas, and

means for distributing a plasma loop voltage in the plasma chamber across multiple dielectric regions to reduce surface erosion in the plasma chamber.

55. The reactive gas source of claim 54 wherein the plasma chamber comprises at least one of a metallic material and a coated metallic material.

56. A reactive gas source for dissociating gases in a toroidal plasma comprising:

a plasma chamber comprising multiple dielectric regions that segment the plasma chamber into portions;

one or more transformers each having a magnetic core surrounding a portion of the plasma chamber and a primary winding;

a gas inlet for providing a feed gas to the plasma chamber; and

a solid state AC switching power supply supplying an AC current to the primary windings of the one or more transformers, the AC current in the primary windings inducing a combined AC potential inside the plasma chamber to form the toroidal plasma that completes a secondary circuit of the transformer and dissociates the feed gas, wherein a plasma loop voltage in the plasma chamber is distributed across multiple dielectric regions to reduce surface erosion in the plasma chamber.

57. The reactive gas source of claim 56 further comprising cooling channels thermally bonded to the plasma chamber for passing a fluid that controls the temperature of the plasma chamber.

58. The reactive gas source of claim 56 wherein the AC switching power supply supplies the AC current to the primary windings without using an impedance matching network.

59. The reactive gas source of claim 56 wherein the AC switching power supply supplies the AC current to the primary windings without using a conventional impedance matching network.

60. The reactive gas source of claim 56 further comprising voltage divider circuit for controlling the distribution the plasma loop voltage across multiple dielectric regions.

61. The reactive gas source of claim 56 wherein the dielectric regions comprise a dielectric spacer protected from the plasma by a protrusion in the plasma chamber.

62. The reactive gas source of claim 56 wherein the plasma loop voltage is reduced to about 100 volts or lower across each of the multiple dielectric regions.

63. The reactive gas source of claim 56 wherein the plasma loop voltage is distributed equally across each of the multiple dielectric regions.

64. The reactive gas source of claim 56 wherein the plasma chamber comprises at least one of a metallic material and a coated metallic material.