Plasma reactor with minimal D.C. coils for cusp, solenoid and mirror fields for plasma uniformity and device damage reduction

• US 20050167051A1
• Filed: 01/28/2005
• Published: 08/04/2005
• Est. Priority Date: 07/09/2002
• Status: Active Grant

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Tavassoli, Hamid F., Horioka, Keiji, Hoffman, Daniel J., Buchberger, Douglas A. Jr., Lindley, Roger A., Kutney, Michael C., Salinas, Martin J.
• Granted Patent: US 8,617,351 B2
• Time in Patent Office: Days
• US Class Current: 156/345.460
• 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 workpiece, includes a vacuum chamber defined by a sidewall and ceiling, and a workpiece support pedestal having a workpiece support surface in the chamber and facing the ceiling and including a cathode electrode. An RF power generator is coupled to the cathode electrode. Plasma distribution is controlled by an external annular inner electromagnet in a first plane overlying the workpiece support surface, an external annular outer electromagnet in a second plane overlying the workpiece support surface and having a greater diameter than the inner electromagnet, and an external annular bottom electromagnet in a third plane underlying the workpiece support surface. D.C. current supplies are connected to respective ones of the inner, outer and bottom electromagnets.

Claims

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

a vacuum chamber comprising a sidewall and a ceiling;

a workpiece support pedestal having a workpiece support surface in said chamber and facing said ceiling and comprising a cathode electrode;

an RF power generator coupled to said cathode electrode;

an external annular inner electromagnet in a first plane overlying said workpiece support surface;

an external annular outer electromagnet in a second plane overlying said workpiece support surface and having a greater diameter than said inner electromagnet;

an external annular bottom electromagnet in a third plane underlying said workpiece support surface; and

inner, outer and bottom D.C. current supplies connected to respective ones of said inner, outer and bottom electromagnets.

2. The reactor of claim 1 wherein said workpiece support pedestal and said inner, outer and bottom magnets are generally coaxial.

3. The reactor of claim 2 wherein said first plane overlies said second plane and both said first and second planes overlie said third plane.

4. The reactor of claim 3 wherein said first, second and third planes are parallel with said workpiece support surface.

5. The reactor of claim 1 further comprising a processor controlling D.C. currents from said inner, outer and bottom D.C. current supplies.

6. The reactor of claim 5 wherein said processor is operable in three modes, comprising:

(a) a cusp mode wherein said D.C. currents cause said bottom electromagnet and one of said inner and outer electromagnets to generate equal and opposite magnetic fields at said workpiece support surface,

(b) a mirror mode wherein said D.C. currents cause said bottom electromagnet and one of said inner and outer electromagnets to generate like magnetic fields at said workpiece support surface, and

(c) a solenoid mode wherein said D.C. current cause at least one of said electromagnets to generate both radial and axial magnetic fields at said workpiece support surface.

7. The reactor of claim 6 wherein said processor is operable in only one of said three modes at one time.

8. The reactor of claim 6 wherein said processor is operable in a selected one of said three modes.

9. The reactor of claim 5 wherein said processor is operable in three modes, comprising:

(a) a cusp mode wherein said bottom electromagnet and one of said inner and outer electromagnets produce a predominantly radial D.C. magnetic field,

(b) a mirror mode wherein said bottom electromagnetic and one of said inner and outer electromagnets produce a predominantly axial magnetic field, and

(c) a solenoidal mode wherein at least one of said electromagnets produces an axial magnetic field and a radial magnetic field.

10. The reactor of claim 9 wherein said processor is operable in a selected one of said three modes.

11. The reactor of claim 9 wherein said processor is operable to produce components of said three modes simultaneously.

29. The reactor of claim 1 wherein said ceiling comprises a capacitively coupled overhead electrode, said reactor further comprising:

a VHF plasma source power generator;

a fixed tuning element coupling said VHF plasma source power generator to said overhead electrode; and

said electrode forming a resonance with plasma in said chamber having a resonant frequency at or near the frequency of said VHF plasma source power generator.

30. The reactor of claim 29 wherein said fixed tuning element comprises a coaxial tuning stub having a stub resonant frequency at or near said resonant frequency.

12. In a plasma reactor having an external annular inner electromagnet in a first plane overlying a workpiece support surface, an external annular outer electromagnet in a second plane overlying the workpiece support surface and having a greater diameter than said inner electromagnet, and an external annular bottom electromagnet in a third plane underlying the workpiece support surface, a method of improving uniformity of plasma ion density distribution, comprising:

generating, from said bottom electromagnet and one of said inner and outer electromagnets, a radial magnetic field at said workpiece support surface having sufficient field strength to increase plasma ion density near a periphery of said workpiece support surface relative to plasma ion density at the center of said workpiece support surface.

13. The method of claim 12 further comprising:

further increasing plasma ion density at said periphery by generating an additional magnetic field component with the other of said inner and outer electromagnets.

14. The method of claim 13 wherein said additional magnetic field component includes an axial magnetic field at said workpiece support surface.

15. The method of claim 14 wherein said axial magnetic field has less field strength than said radial magnetic field at said workpiece support surface.

16. The method of claim 12 further comprising:

prior to processing a production workpiece, finding a solenoidal magnetic field that produces a desired uniformity of plasma ion density radial distribution and determining a radial component of said solenoidal field; and

wherein the step of generating said radial magnetic field comprises increasing said radial magnetic field beyond the strength of said radial component of said solenoidal magnetic field until plasma ion density radial distribution uniformity at least nearly reaches said desired uniformity produced by said solenoidal magnetic field.

17. In a plasma reactor having an external annular inner electromagnet in a first plane overlying a workpiece support surface, an external annular outer electromagnet in a second plane overlying the workpiece support surface and having a greater diameter than said inner electromagnet, and an external annular bottom electromagnet in a third plane underlying the workpiece support surface, a method of controlling plasma ion density distribution, comprising:

generating, from said bottom electromagnet and one of said inner and outer electromagnets, a radial magnetic field at said workpiece support surface having sufficient field strength to increase plasma ion density near a periphery of said workpiece support surface relative to plasma ion density at the center of said workpiece support surface; and

generating from the other of said inner and outer electromagnets an axial magnetic field at said workpiece support surface that is of a minimal strength to attain a more uniform radial distribution of plasma ion density.

18. The reactor of claim 17 wherein plasma ion density is determined from etch rate radial distributions on production wafers processed at said workpiece support surface.

19. In a plasma reactor having an external annular inner electromagnet in a first plane overlying a workpiece support surface, an external annular outer electromagnet in a second plane overlying the workpiece support surface and having a greater diameter than said inner electromagnet, and an external annular bottom electromagnet in a third plane underlying the workpiece support surface, a method of controlling plasma ion density distribution, comprising:

finding a set of D.C. current pairs applied to a pair of said inner, outer and bottom magnets that tends to minimize plasma ion density distribution nonuniformity;

for each one of said D.C. current pairs of said set, finding a D.C. current applied to the other of said inner, outer and bottom electromagnets that tends to minimize plasma ion density distribution nonuniformity, so as to establish a set of D.C. current triplets corresponding to said inner, outer and bottom magnets; and

applying one of said D.C. current triplets to said inner, outer and bottom magnets.

20. The method of claim 19 wherein said pair of said inner, outer and bottom electromagnets comprises said bottom electromagnet and one of said inner and outer electromagnets, whereby said pair of electromagnets establishes a predominantly radial magnetic field at said workpiece support surface and said other magnet establishes a smaller axial magnetic field.

21. The method of claim 20 wherein said pair of inner, outer and bottom electromagnets comprises said bottom electromagnet and said outer electromagnet, and said other electromagnet comprises said inner electromagnet.

22. The method of claim 19 wherein plasma ion density distribution is inferred from measured radial distribution of etch rate on semiconductor wafers processed at said workpiece support surface.

23. In a plasma reactor having an external annular inner electromagnet in a first plane overlying a workpiece support surface, an external annular outer electromagnet in a second plane overlying the workpiece support surface and having a greater diameter than said inner electromagnet, and an external annular bottom electromagnet in a third plane underlying the workpiece support surface, a method of controlling plasma ion density distribution, comprising:

determining an uncorrected plasma ion density distribution at said workpiece support surface;

determining change in plasma ion density distribution as functions of D.C. current applied singly to each individual ones of said inner, outer and bottom electromagnets;

superimpose said functions on said uncorrected plasma distribution for different combinations of D.C. currents applied to said inner, outer and bottom electromagnets, to obtain plural trial plasma ion density distributions;

searching said trial plasma ion density distributions for at least one having a high uniformity of plasma ion density distribution and determining the optimum set of currents corresponding thereto; and

applying said optimum set of currents to respective ones of said inner, outer and bottom electromagnets.

24. The method of claim 23 wherein the steps of determining plasma ion density distributions comprise inferring said plasma ion density distributions from measured etch rate distributions on semiconductor wafers processed at said workpiece support surface.

25. A plasma reactor for processing a workpiece on a workpiece support surface within a reactor chamber, comprising:

an external annular inner electromagnet in a first plane overlying said workpiece support surface;

an external annular outer electromagnet in a second plane overlying the workpiece support surface and having a greater diameter than said inner electromagnet;

an external annular bottom electromagnet in a third plane underlying the workpiece support surface;

a processor in control of D.C. currents applied to respective ones of said inner, outer and bottom electromagnets; and

a memory accessible to said processor, said memory storing values of D.C. currents for respective ones of said inner, outer and bottom electromagnets, said currents having been determined by a process comprising;

finding a set of D.C. current pairs applied to a pair of said inner, outer and bottom magnets that tends to minimize plasma ion density distribution nonuniformity;

for each one of said D.C. current pairs of said set, finding a D.C. current applied to the other of said inner, outer and bottom electromagnets that tends to minimize plasma ion density distribution nonuniformity, so as to establish a set of D.C. current triplets corresponding to said inner, outer and bottom magnets.

26. The reactor of claim 25 wherein plasma ion density distribution is inferred from etch rate distribution measured on wafers processed at said workpiece support surface.

27. A plasma reactor for processing a workpiece on a workpiece support surface within a reactor chamber, comprising:

an external annular inner electromagnet in a first plane overlying said workpiece support surface;

an external annular outer electromagnet in a second plane overlying the workpiece support surface and having a greater diameter than said inner electromagnet;

an external annular bottom electromagnet in a third plane underlying the workpiece support surface;

a processor in control of D.C. currents applied to respective ones of said inner, outer and bottom electromagnets; and

a memory accessible to said processor, said memory storing values of D.C. currents for respective ones of said inner, outer and bottom electromagnets, said currents having been determined by a process comprising;

determining an uncorrected plasma ion density distribution at said workpiece support surface;

determining change in plasma ion density distribution as functions of D.C. current applied singly to each individual ones of said inner, outer and bottom electromagnets;

superimpose said functions on said uncorrected plasma distribution for different combinations of D.C. currents applied to said inner, outer and bottom electromagnets, to obtain plural trial plasma ion density distributions;

searching said trial plasma ion density distributions for at least one having a high uniformity of plasma ion density distribution and determining the optimum set of currents corresponding thereto.

28. The reactor of claim 27 wherein plasma ion density distribution is inferred from etch rate distribution measured on wafers processed at said workpiece support surface.