Plasma Immersion Ion Source With Low Effective Antenna Voltage

Abstract

A plasma source includes a chamber that contains a process gas. The chamber includes a dielectric window that passes electromagnetic radiation. A RF power supply generates a RF signal. At least one RF antenna with a reduced effective antenna voltage is connected to the RF power supply. The at least one RF antenna is positioned proximate to the dielectric window so that the RF signal electromagnetically couples into the chamber to excite and ionize the process gas, thereby forming a plasma in the chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The aspects of this invention may be better understood by referring to the following description in conjunction with the accompanied drawings, in which like numerals indicate like structural elements and features in various figures. The drawings are not necessarily to scale. A skilled artisan will understand that the drawings, described below, are for illustration purposes only. The drawings are not intended to limit the scope of the present teachings in any way.

FIG. 1 illustrates one embodiment of a RF plasma source for a plasma doping apparatus according to the present invention.

FIG. 2 is a schematic diagram of a plasma source power system including a termination according to the present invention that reduces the energy of ions in the plasma and thus metal contamination caused by sputtering the dielectric window.

FIG. 3A illustrates a bottom view of one embodiment of the planar antenna coil of the RF plasma source according to the present invention.

FIG. 3B illustrates a cross sectional view a portion of a plasma source according to the present invention including a Faraday shield on only the planar antenna coil.

FIG. 3C illustrates a cross sectional view a portion of a plasma source according to the present invention that includes Faraday shields on both the planar and the helical antenna coils.

FIG. 4 illustrates a capacitance model of one embodiment of a RF plasma generator according to the present invention that includes a low dielectric constant material that forms a capacitive voltage divider which lowers the effective RF antenna voltage.

Claims

1. A plasma source comprising: a) a chamber that contains a process gas, the chamber comprising a dielectric window that passes electromagnetic radiation;b) a RF power supply that generates a RF signal at an output; andc) at least one RF antenna having an input that is electrically connected to the output of the RF power supply and an output that is terminated with an impedance that reduces an effective RF antenna voltage, the at least one RF antenna being positioned proximate to the dielectric window so that the RF signal electromagnetically couples into the chamber to excite and ionize the process gas, thereby forming a plasma in the chamber.

2. The plasma source of claim 1 wherein the impedance that reduces the effective RF antenna voltage comprises a capacitive reactance.

3. The plasma source of claim 2 wherein the capacitive reactance comprises a capacitor having a variable capacitance.

4. The plasma source of claim 1 wherein the at least one RF antenna comprises one of a planar coil RF antenna and a helical coil RF antenna.

5. The plasma source of claim 1 wherein the at least one RF antenna comprises both a planar coil RF antenna and a helical coil RF antenna.

6. The plasma source of claim 5 wherein the planer coil RF antenna and the helical coil RF antenna are electrically connected.

7. The plasma source of claim 5 wherein the planer coil RF antenna and the helical coil RF antenna are electromagnetically coupled.

8. The plasma source of claim 1 further comprising a dielectric material positioned between the at least one RF antenna and the dielectric window so as to form a capacitive voltage divider that further reduces the effective RF antenna voltage.

9. The plasma source of claim 1 further comprising a Faraday shield surrounding at least a portion of the at least one RF antenna.

10. The plasma source of claim 9 wherein the Faraday shield comprises a conductive coating deposited over a dielectric material on the at least one RF antenna.

11. The plasma source of claim 1 wherein the Faraday shield is electrically floating during plasma ignition and is coupled to ground potential after plasma ignition.

12. A plasma source comprising: a) a chamber that contains a process gas, the chamber comprising a dielectric window that passes electromagnetic radiation;b) a RF power supply that generates a RF signal at an output;c) at least one RF antenna having an input that is electrically connected to the output of the RF power supply, the at least one RF antenna being positioned proximate to the dielectric window so that the RF signal electromagnetically couples into the chamber to excite and ionize the process gas, thereby forming a plasma in the chamber; andd) a dielectric material positioned between the at least one RF antenna and the dielectric window so as to form a capacitive voltage divider that reduces an effective RF antenna voltage.

13. The plasma source of claim 12 wherein the at least one RF antenna comprises one of a planar coil RF antenna and a helical coil RF antenna.

14. The plasma source of claim 12 wherein the at least one RF antenna comprises both a planar coil RF antenna and a helical coil RF antenna.

15. The plasma source of claim 14 wherein the planer coil RF antenna and the helical coil RF antenna are electrically connected.

16. The plasma source of claim 14 wherein the planer coil RF antenna and the helical coil RF antenna are electromagnetically coupled.

17. The plasma source of claim 12 wherein the dielectric material positioned between the at least one RF antenna and the dielectric window comprises potting material that is deposited on an outer surface of the at least one RF antenna.

18. The plasma source of claim 17 wherein the potting material comprises a thermally conducting elastomer.

19. The plasma source of claim 12 wherein an output of the at least one RF antenna is terminated with an impedance that further reduces the effective RF antenna voltage.

20. The plasma source of claim 19 wherein the impedance that further reduces the effective RF antenna voltage comprises a capacitive reactance.

21. The plasma source of claim 12 further comprising a Faraday shield that is positioned between at least a portion of the at least one RF antenna and the dielectric window.

22. The plasma source of claim 21 wherein the Faraday shield comprises a conductive coating deposited over the dielectric material forming the capacitive voltage divider, the conductive material defining at least one gap for transmitting the RF signal.

23. The plasma source of claim 21 wherein the Faraday shield is electrically floating during plasma ignition and coupled to ground potential after plasma ignition.

24. A plasma source comprising: a) a chamber that contains a process gas, the chamber comprising a dielectric window that passes electromagnetic radiation;b) a RF power supply that generates a RF signal at an output;c) at least one RF antenna having an input that is electrically connected to the output of the RF power supply, the at least one RF antenna being positioned proximate to the dielectric window so that the RF signal electromagnetically couples into the chamber to excite and ionize the process gas, thereby forming a plasma in the chamber; andd) a Faraday shield positioned between at least a portion of the RF antenna and the dielectric window, the Faraday shield reducing an effective RF antenna voltage.

25. The plasma source of claim 24 wherein the at least one RF antenna comprises one of a planar coil RF antenna and a helical RF antenna.

26. The plasma source of claim 24 wherein the at least one RF antenna comprises both a planar coil RF antenna and a helical coil RF antenna.

27. The plasma source of claim 26 wherein the planer coil RF antenna and the helical coil RF antenna are electrically connected.

28. The plasma source of claim 26 wherein the planer coil RF antenna and the helical coil RF antenna are electromagnetically coupled.

29. The plasma source of claim 24 wherein the Faraday shield comprises a conductive coating that defines at least one gap for transmitting the RF signal.

30. The plasma source of claim 24 wherein the Faraday shield is electrically floating during plasma ignition and coupled to ground potential after plasma ignition.

31. The plasma source of claim 24 further comprising a dielectric material positioned between the at least one RF antenna and the Faraday shield so as to form a capacitive voltage divider that reduces the effective RF antenna voltage.

32. A method of generating a plasma, the method comprising: a) containing a process gas in a chamber;b) generating a RF signal;c) reducing an effective antenna voltage of at least one RF antenna;d) propagating the RF signal through the at least one RF antenna with the reduced effective antenna voltage; ande) coupling the RF signal from the at least one RF antenna through a dielectric window to excite and ionize the process gas, thereby forming a plasma in the chamber.

33. The method of claim 32 wherein the reducing the effective antenna voltage comprises coupling the RF signal through a capacitive voltage divider.

34. The method of claim 32 wherein the reducing the effective antenna voltage comprises partially shielding the RF signal from the dielectric window.

35. The method of claim 32 wherein the reducing the effective antenna voltage comprises terminating the RF antenna with a capacitive reactance.