Capacitively coupled plasma reactor with uniform radial distribution of plasma

• US 6,900,596 B2
• Filed: 09/04/2002
• Issued: 05/31/2005
• Est. Priority Date: 07/09/2002
• Status: Expired due to Term

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Hoffman, Daniel J., Buchberger, Douglas A. Jr., Miller, Matthew L., Chiang, Kang-Lie, Delgadino, Gerardo A., Carducci, James D., Yang, Jang Gyoo
• Primary Examiner(s): Wong, Don K.
• Assistant Examiner(s): VU, JIMMY T
• Application Number:
  US10/235,988
• Publication Number:
  US 20040056602A1
• Time in Patent Office: 1,000 Days
• Field of Search: 315/11.21, 315/111.41, 315/111.51, 315/111.81, 343/895, 343/867, 118/723.I, 118/723.E, 118/723.R, 118/723.M, 156/345
• US Class Current: 315/111.21
• 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 37/32091 the radio frequency energy being capacitively coupled to the plasma
• CPC Class Codes: H01J 37/3244 Gas supply means
• CPC Class Codes: H01J 37/32623 Mechanical discharge control means
• CPC Class Codes: H01J 37/3266 Magnetic control means

Abstract

A plasma reactor for processing a semiconductor wafer includes a side wall and an overhead ceiling defining a chamber, a workpiece support cathode within the chamber having a working surface facing the ceiling for supporting a semiconductor workpiece, process gas inlets for introducing a process gas into the chamber and an RF bias power generator having a bias power frequency. There is a bias power feed point at the working surface and an RF conductor is connected between the RF bias power generator and the bias power feed point at the working surface. A dielectric sleeve surrounds a portion of the RF conductor, the sleeve having an axial length along the RF conductor, a dielectric constant and an axial location along the RF conductor, the length, dielectric constant and location of the sleeve being such that the sleeve provides a reactance that enhances plasma ion density uniformity over the working surface. In accordance with a further aspect, the reactor can include an annular RF coupling ring having an inner diameter corresponding generally to a periphery of the workpiece, the RF coupling ring extending a sufficient portion of a distance between the working surface and the overhead electrode to enhance plasma ion density near a periphery of the workpiece.

Claims

1. A plasma reactor comprising:

a side wall and an overhead ceiling defining a chamber;

a workpiece support cathode within the chamber having a working surface facing said ceiling for supporting a semiconductor workpiece;

process gas inlets for introducing a process gas into said chamber;

an RF bias power generator having a bias power frequency;

a bias power feed point at said working surface;

an RF conductor connected between said RF bias power generator and said bias power feed point at said working surface; and

a dielectric sleeve surrounding a portion of said RF conductor, said sleeve having an axial length along said RF conductor, a dielectric constant and an axial location along said RF conductor, said length, dielectric constant and location of said sleeve being such that said sleeve provides a reactance that enhances plasma ion density uniformity over said working surface.

2. The reactor of claim 1 wherein said feed point has an impedance at said bias power frequency, and wherein the reactance provided by said dielectric sleeve brings the impedance of said feed point at said bias power frequency to a value closer to an impedance of a portion of said workpiece support cathode surrounding said RF conductor and sleeve.

3. The reactor of claim 1 wherein:

said cathode comprises a planar insulation layer having a top surface comprising said working surface and a planar conductive layer within said planar insulation layer;

said feed point has an impedance at said bias power frequency; and

the reactance provided by said dielectric sleeve brings the impedance of said feed point at said bias power frequency to a value closer to an impedance of said conductive layer at said bias power frequency.

4. The reactor of claim 2 wherein said ceiling comprises an overhead electrode, said reactor further comprising:

a source power generator having a source frequency;

an impedance match element connected between said source power generator and said overhead electrode;

said feed point has an impedance at said source power frequency;

wherein the reactance of said sleeve brings the impedance of said feed point at said source frequency to a value closer to an impedance of zero.

5. The reactor of claim 3 wherein said ceiling comprises an overhead electrode, said reactor further comprising:

a source power generator having a source frequency;

an impedance match element connected between said source power generator and said overhead electrode;

wherein said feed point has an impedance at said source power frequency; and

wherein the reactance provided by said dielectric sleeve brings the impedance of said feed point at said source power frequency to a value closer to an impedance of zero at said source power frequency.

6. The plasma reactor of claim 1 wherein said sleeve is divided along its axial length into plural sections, the axial length and dielectric constant of each of said sections being independent of the other sections.

7. The plasma reactor of claim 6 wherein the dielectric constants and axial lengths of said sections are such as to bring said feed point impedance at said bias frequency closer to said impedance of said conductive layer at said bias frequency while simultaneously bringing said feed point impedance at said source power frequency closer to an impedance of zero.

8. The reactor of claim 7 wherein said bias power frequency is an HF frequency and said source power frequency is a VHF frequency.

9. The reactor of claim 8 wherein at least one of said plural sleeve sections is formed of alumina while another one of said plural sleeve sections is formed of polytetrafluoroethylene.

10. The reactor of claim 8 wherein a top section of said sleeve comprises a first dielectric material, a middle section of said sleeve comprises a second dielectric material and a bottom section of said sleeve comprises said first dielectric material.

11. The reactor of claim 10 wherein said first dielectric material comprises polytetrafluoroethylene and said second dielectric material comprises alumina.

12. The reactor of claim 8 wherein said overhead electrode has a resonance with a plasma in said chamber at a plasma resonant frequency and wherein said VHF source power frequency is at or near said plasma resonant frequency.

13. The reactor of claim 12 wherein the impedance match element connected between said source power generator and said overhead electrode comprises a fixed tuning stub having a stub resonant frequency at or near said VHF source power frequency.

14. The reactor of claim 13 wherein said stub resonant frequency, said VHF source power frequency and said plasma resonant frequency are near one another and offset from one another.

15. The reactor of claim 5 further comprising:

plural overhead coils of different radii and at different heights above said ceiling and a controller for applying respective D.C. currents to said plural coils so as to enhance uniformity of plasma ion density distribution in said chamber.

16. The reactor of claim 1 further comprising:

an annular RF coupling ring having an inner diameter corresponding generally to a periphery of said workpiece, said RF coupling ring extending a sufficient portion of a distance between said working surface and said overhead electrode to enhance plasma ion density near a periphery of said workpiece.

17. The reactor of claim 16 wherein said RF coupling ring is attached to said working surface and has a top surface extending above said working surface by a thickness of said coupling ring.

18. The reactor of claim 16 wherein said RF coupling ring is attached to said ceiling and has a bottom surface extending below said ceiling by a thickness of said coupling ring.

19. The reactor of claim 17 further comprising a second RF coupling ring overlying said first RF coupling ring and attached to said ceiling.

20. The reactor of claim 16 further comprising:

plural overhead coils of different radii and at different heights above said ceiling and a controller for applying respective D.C. currents to said plural coils so as to enhance uniformity of plasma ion density distribution in said chamber.

21. A plasma reactor comprising:

a side wall and an overhead ceiling defining a chamber, said overhead ceiling comprising an overhead electrode;

a workpiece support cathode within said chamber having a working surface facing said ceiling for supporting a semiconductor workpiece;

process gas inlets for introducing a process gas into said chamber;

an RF bias power generator having a bias power frequency;

a bias power feed point at said working surface;

an RF conductor connected between said RF bias power generator and said bias power feed point and a dielectric sleeve surrounding a section of length of said conductor;

a source power generator having a source frequency;

an impedance match element connected between said source power generator and said overhead electrode;

said feed point having an impedance at said source power frequency;

wherein the reactance of said sleeve reduces the impedance of said feed point at said source frequency to at least nearly zero Ohms.

22. The reactor of claim 21 wherein:

said cathode comprises a planar insulation layer having a top surface comprising said working surface and a planar conductive layer within said planar insulation layer;

the reactance of said dielectric sleeve brings the impedance of said feed point at said bias power frequency to a value closer to an impedance of said conductive layer at said bias power frequency.

23. The reactor of claim 21 wherein said overhead electrode resonates with a plasma at a plasma resonant frequency and wherein said source power frequency is at or near said plasma resonant frequency.

24. The reactor of claim 23 wherein the impedance match element connected between said source power generator and said overhead electrode comprises a fixed tuning stub having a stub resonant frequency at or near said source power frequency.

25. The reactor of claim 24 wherein said stub resonant frequency, said source power frequency and said plasma resonant frequency are near one another and offset from one another.

26. The reactor of claim 24 wherein said plasma resonant frequency, said source power frequency and said stub resonant frequency are all VHF frequencies.

27. The reactor of claim 21 further comprising:

plural overhead coils of different radii and at different heights above said ceiling and a controller for applying respective D.C. currents to said plural coils so as to enhance uniformity of plasma ion density distribution in said chamber.

28. The reactor of claim 21 further comprising:

an annular RF coupling ring having an inner diameter corresponding generally to a periphery of said workpiece, said RF coupling ring extending a sufficient portion of a distance between said working surface and said overhead electrode to enhance plasma ion density near a periphery of said workpiece.

29. The reactor of claim 28 wherein said RF coupling ring is attached to said working surface and has a top surface extending above said working surface by a thickness of said coupling ring.

30. The reactor of claim 28 wherein said RF coupling ring is attached to said ceiling and has a bottom surface extending below said ceiling by a thickness of said coupling ring.

31. The reactor of claim 29 further comprising a second RF coupling ring overlying said first RF coupling ring and attached to said ceiling.

32. The reactor of claim 28 further comprising:

plural overhead coils of different radii and at different heights above said ceiling and a controller for applying respective D.C. currents to said plural coils so as to enhance uniformity of plasma ion density distribution in said chamber.

33. A plasma reactor comprising:

a vacuum enclosure including a side wall and a ceiling defining a vacuum chamber, and a workpiece support within said chamber having a working surface facing said ceiling for supporting a planar workpiece, said workpiece support and said ceiling together defining a processing region between said workpiece support and said ceiling;

process gas inlets for furnishing process gas into said chamber;

an RF bias power generator having a bias frequency;

at least a first overhead solenoidal electromagnet adjacent said ceiling, said overhead solenoidal electromagnet, said ceiling, said sidewall and said workpiece support being located along a common axis of symmetry; and

a current source connected to said first solenoidal electromagnet and furnishing a first electric current in said first solenoidal electromagnet whereby to generate within said chamber a magnetic field which is a function of said first electric current, said first electric current having a value such that said magnetic field increases uniformity of plasma ion density radial distribution about said axis of symmetry near said working surface;

a bias power feed point at said working surface;

an RF conductor connected between said RF bias power generator and said bias power feed point at said working surface; and

a dielectric sleeve surrounding a portion of said RF conductor, said sleeve having an axial length along said RF conductor, a dielectric constant and an axial location along said RF conductor, said length, dielectric constant and location of said sleeve being such that said sleeve provides a reactance that enhances plasma ion density uniformity over said working surface.

34. The reactor of claim 33 wherein said feed point has an impedance at said bias power frequency, and wherein the reactance provided by said dielectric sleeve brings the impedance of said feed point at said bias power frequency to a value closer to an impedance of a portion of said workpiece support cathode surrounding said RF conductor and sleeve.

35. The reactor of claim 33 wherein:

said cathode comprises a planar insulation layer having a top surface comprising said working surface and a planar conductive layer within said planar insulation layer;

said feed point has an impedance at said bias power frequency; and

the reactance provided by said dielectric sleeve brings the impedance of said feed point at said bias power frequency to a value closer to an impedance of said conductive layer at said bias power frequency.

36. The reactor of claim 35 wherein said ceiling comprises an overhead electrode, said reactor further comprising:

a source power generator having a source frequency;

an impedance match element connected between said source power generator and said overhead electrode;

said feed point has an impedance at said source power frequency;

wherein the reactance of said sleeve brings the impedance of said feed point at said source frequency to a value closer to an impedance of zero.

37. The reactor of claim 33 wherein said first solenoidal electromagnet is outside of said chamber and faces an external surface of said ceiling.

38. The reactor of claim 36 wherein said source power generator provides an RF power level that maintains a plasma within said chamber at a desired plasma ion density level;

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.

39. The reactor of claim 33 further comprising a plurality of overhead solenoidal magnets adjacent said ceiling having a combined static magnetic field in said chamber comprising a sum of individual static magnetic fields produced by respective ones of said plurality of solenoidal magnets, wherein said overhead solendoid, said ceiling, said sidewall and said workpiece support are located along a common axis of symmetry, said first overhead solenoidal magnet being comprised within said plurality of overhead solenoidal magnets;

and

wherein said combined magnetic field increases uniformity of plasma ion density radial distribution about said axis of symmetry near a surface of said workpiece support.

40. The reactor of claim 39 wherein said plurality of solenoidal magnets are concentric and are arranged in order of ascending diameter and descending axial height above said ceiling.

41. The reactor of claim 40 wherein:

the outermost ones of said magnets exert a correspondingly greater radial magnetic pressure on plasma across a greater radial area than the innermost ones of said magnets;

the innermost ones of said magnets exert radial magnetic pressure on plasma within a region confined near the center of said chamber.

42. The reactor of claim 36 wherein said plasma has a reactance and the reactance of said electrode corresponds to the reactance of said plasma.

43. The reactor of claim 42 wherein the reactance of said electrode is a conjugate of the reactance of said plasma.

44. The reactor of claim 42 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.

45. The reactor of claim 42 wherein the frequency of said RF generator and the electrode-plasma resonant frequency are VHF frequencies.

46. The reactor of claim 42 further comprising a fixed impedance matching element connected between said generator and said overhead electrode, said fixed impedance match element having a match element resonant frequency.

47. The reactor of claim 46 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.

48. The reactor of claim 47 wherein said frequency of said generator, said plasma frequency and said match element resonant frequency are all VHF frequencies.

49. The reactor of claim 47 wherein said frequency of said RF power generator, said match element resonant frequency and said electrode-plasma resonant frequency are all VHF frequencies offset from one another.

50. The reactor of claim 33 further comprising:

an annular RF coupling ring having an inner diameter corresponding generally to a periphery of said workpiece, said RF coupling ring extending a sufficient portion of a distance between said working surface and said overhead electrode to enhance plasma ion density near a periphery of said workpiece.

51. The reactor of claim 50 wherein said RF coupling ring is attached to said working surface and has a top surface extending above said working surface by a thickness of said coupling ring.

52. The reactor of claim 50 wherein said RF coupling ring is attached to said ceiling and has a bottom surface extending below said ceiling by a thickness of said coupling ring.

53. The reactor of claim 51 further comprising a second RF coupling ring overlying said first RF coupling ring and attached to said ceiling.