Merie plasma reactor with overhead RF electrode tuned to the plasma with arcing suppression

• US 20040211759A1
• Filed: 10/22/2001
• Published: 10/28/2004
• Est. Priority Date: 03/17/2000
• Status: Active Grant

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Ye, Yan, Hoffman, Daniel J., Buchberger, Douglas A. Jr., Miller, Matthew L., Katz, Dan, Zhao, Xiaoye, Chiang, Kang-Lie, Hagen, Robert B.
• Granted Patent: US 6,894,245 B2
• Time in Patent Office: Days
• US Class Current: 219/121.43
• 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 37/32183 Matching circuits
• CPC Class Codes: H01J 37/3244 Gas supply means
• CPC Class Codes: H01J 37/3266 Magnetic control means

Abstract

A plasma reactor for processing a semiconductor workpiece, includes a reactor chamber having a chamber wall and containing a workpiece support for holding the semiconductor support, the electrode comprising a portion of the chamber wall, an RF power generator for supplying power at a frequency of the generator to the overhead electrode and capable of maintaining a plasma within the chamber at a desired plasma ion density level. The overhead electrode has a capacitance such that the overhead electrode and the plasma formed in the chamber at the desired plasma ion density resonate together at an electrode-plasma resonant frequency, the frequency of the generator being at least near the electrode-plasma resonant frequency. The reactor further includes a set of MERIE magnets surrounding the plasma process area overlying the wafer surface that produce a slowly circulating magnetic field which stirs the plasma to improve plasma ion density distribution uniformity.

Claims

1. A plasma reactor for processing a semiconductor workpiece, comprising:

a reactor chamber having a chamber wall and containing a workpiece support for holding the semiconductor workpiece;

an overhead electrode overlying said workpiece support;

an RF power generator for supplying power at a frequency of said generator;

said overhead electrode having a reactance that forms a resonance with the plasma at an electrode-plasma resonant frequency which is at or near said frequency of said generator;

a magnetic field generator for producing a controllable magnetic field over the surface of said workpiece; and

a fixed impedance matching element coupled to said RF power generator and to said overhead electrode.

2. The reactor of claim 1 wherein said magnetic field is sufficiently small in magnitude so that the electron cyclotron frequency associated with said magnetic field is less than the frequency of said RF power generator.

3. The reactor of claim 2 wherein said electron cyclotron frequency is at least 5% less than said RF power generator frequency.

4. The reactor of claim 2 wherein said frequency of said RF power generator is a VHF frequency.

5. The reactor of claim 1 further comprising:

an insulating layer formed on a surface of said overhead electrode facing said workpiece support.

6. The reactor of claim 5 further comprising:

a capacitive insulating layer between said RF power generator and said overhead electrode.

7. The reactor of claim 6 further comprising:

a metal foam layer overlying and contacting a surface of said overhead electrode that faces away from said workpiece support.

8. The reactor of claim 5 further comprising a silicon-containing coating covering said insulating layer.

9. The reactor of claim 8 wherein said silicon-containing coating comprises one of silicon or silicon carbide.

10. The reactor of claim 7 wherein said insulating layer provides a capacitance sufficient to suppress arcing within said gas injection ports.

11. The reactor of claim 10 wherein said capacitive insulating layer has a sufficient capacitance to block D.C. current from a plasma within said chamber from flowing through said overhead electrode.

12. The reactor of claim 11 wherein:

said electrode has plural gas injection orifices therein generally facing said workpiece support; and

said metal foam layer is of a sufficient thickness to suppress an axial electric field within said gas injection orifices.

13. The reactor of claim 5 wherein said overhead electrode comprises aluminum and said insulating layer is formed by anodization.

14. The reactor of claim 6 wherein said capacitive insulating layer forms a capacitance that provides a low impedance path to ground through said overhead electrode for plasma sheath generated harmonics.

15. The reactor of claim 6 further comprising:

a gas inlet to said overhead electrode;

a gas baffling layer within said overhead electrode between said gas inlet and at least a first set of said gas injection orifices.

16. The reactor of claim 15 wherein said gas baffling layer comprises a layer of metal foam.

17. The reactor of claim 13 further comprising thermal control fluid passages within said overhead electrode.

18. The reactor of claim 17 further comprising an optical window in said overhead electrode generally facing said wafer support and a light carrying medium coupled to said window and extending through said overhead electrode.

19. The reactor of claim 5 wherein said plasma has a reactance and the reactance of said electrode corresponds to the reactance of said plasma.

20. The reactor of claim 19 wherein the reactance of said electrode is a conjugate of the reactance of said plasma.

21. The reactor of claim 19 wherein the reactance of said plasma comprises a negative capacitance, and wherein the capacitance of said electrode is the same magnitude as the magnitude of said negative capacitance of said plasma.

22. The reactor of claim 1 wherein the frequency of said RF generator and the electrode-plasma resonant frequency are VHF frequencies.

23. The reactor of claim 22 wherein said plasma reactance is a function of said plasma ion density and said plasma ion density supports a selected plasma process of said reactor.

24. The reactor of claim 23 wherein said plasma process is a plasma etch process and wherein said plasma ion density lies in a range from about 10⁹ ions/cubic centimeter to about 10¹² ions/cubic centimeter.

25. The reactor of claim 1 wherein said fixed impedance match element has a match element resonant frequency.

26. The reactor of claim 25 wherein the match element resonant frequency and said electrode-plasma resonant frequency are offset from one another and the frequency of said generator lies between said electrode-plasma resonant frequency and said match element resonant frequency.

27. The reactor of claim 26 wherein said frequency of said generator, said plasma frequency and said match element resonant frequency are all VHF frequencies.

28. The reactor of claim 25 wherein said fixed impedance match element comprises:

a strip line circuit having a near end thereof adjacent said overhead electrode for coupling power from said RF power generator to said overhead electrode and providing an impedance transformation therebetween, said strip line circuit comprising;

a strip line conductor generally above said overhead electrode and connected at a near end thereof to said overhead electrode,

a ground plane conductor above said overhead electrode and spaced from said inner conductor along the length thereof and connected to an RF return potential of said RF power generator,

a tap at a selected location along the length of said strip line conductor, said tap comprising a connection between said strip line conductor and an output terminal of said RF power generator.

31. The reactor of claim 1 wherein said VHF frequency is suitable for capacitively coupling plasma source power.

29. The reactor of 28 wherein said ground plane conductor comprises a ceiling of a housing overlying said overhead electrode, said strip line conductor formed along a winding path within said housing and beneath said ceiling.

30. The reactor of claim 29 wherein said strip line conductor is hollow, said reactor further comprising:

a gas feed line extending through said hollow strip line conductor for supplying process gas to said gas injection orifices in said overhead electrode.