Distributed inductively-coupled plasma source

• US 6,273,022 B1
• Filed: 03/14/1998
• Issued: 08/14/2001
• Est. Priority Date: 03/14/1998
• Status: Expired due to Fees

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Pu, Bryan Y., Welch, Mike, Bjorkman, Claes, Doan, Kenny, Shan, Hongching, Mett, Richard Raymond
• Primary Examiner(s): Mills, Gregory
• Assistant Examiner(s): Zervigon, Rudy
• Application Number:
  US09/039,216
• Time in Patent Office: 1,249 Days
• Field of Search: 438/725, 315/248, 315/57, 156/345, 118/223.MA, 216/68, 505/1, 75/11
• US Class Current: 118/723.00I
• CPC Class Codes: H01J 37/321 the radio frequency energy being inductively coupled to the plasma

Abstract

Apparatus and method for inductively coupling electrical power to a plasma in a semiconductor process chamber. In a first aspect, an array of induction coils is distributed over a geometric surface having a circular transverse section. Each coil has a transverse section which is wedge-shaped so that the adjacent sides of any two adjacent coils in the array are approximately parallel to a radius of the circular transverse section of the geometric surface. The sides of adjacent coils being parallel enhances the radial uniformity of the magnetic field produced by the coil array. In a second aspect, electrostatic coupling between the induction coils and the plasma is minimized by connecting each induction coil to the power supply so that the turn of wire of the coil which is nearest to the plasma is near electrical ground potential. In one embodiment, the near end of each coil connects directly to electrical ground. In second and third embodiments, two coils are connected in series at the near end of each coil. In the second embodiment, the opposite (“RF hot”) end of each coil is connected to a respective balanced output of an RF power supply. In the third embodiment, the hot end of one coil is connected to the unbalanced output of an RF power supply, and the hot end of the other coil is connected to electrical ground through a capacitor which resonates with the latter coil at the frequency of the RF power supply.

Claims

1. A plasma chamber for fabricating semiconductors, comprising:

an enclosure for sealing an interior volume so as to withstand a vacuum in said interior;

an RF power supply;

a plurality of induction coils connected to receive electrical power from the RP power supply so that the coils produce a magnetic field in a portion of said interior, wherein

each coil has an axial end positioned adjacent a first geometric surface having a circular transverse section,

the coils are equally spaced azimuthally relative to said circular transverse section of the first geometric surface, and

each coil has a transverse section which is wedge-shaped so that the adjacent sides of any two adjacent coils are approximately parallel to a radius of the circular transverse section of the geometric surface.

2. A plasma chamber according to claim 1, wherein:

the geometric surface is a surface of a circular dielectric wall of the enclosure; and

the induction coils are positioned adjacent to and outside of the circular wall.

3. A plasma chamber according to claim 1, wherein:

each coil has a longitudinal axis around which that coil is wound; and

the longitudinal axis of each coil is generally perpendicular to the first geometric surface.

4. A plasma chamber according to claim 1, wherein the power supply is connected to supply electrical power to the respective induction coils in respective polarities such that any two adjacent induction coils produce respective magnetic fields of opposite polarity.

5. A plasma chamber according to claim 4, further comprising:

a chuck for holding a semiconductor workpiece at a position in the chamber which is a distance from the induction coils;

wherein the induction coils are spaced apart by an azimuthal gap which is sufficiently small, relative to the distance between the coils and the workpiece position, so that the strength of any magnetic field produced by the coils is at least ten times smaller at the workpiece position than at another position within the plasma chamber which is closer to the coils.

31. A plasma chamber according to claim 1, further comprising:

a chuck for holding a semiconductor workpiece parallel to the geometric surface.

32. A plasma chamber according to claim 5, wherein the chuck holds the semiconductor workpiece parallel to the geometric surface.

33. A plasma chamber according to claim 4, wherein:

for any two adjacent coils, one of said two adjacent coils is wound clockwise, and the other one of said two adjacent coils is wound counterclockwise.

35. A plasma chamber according to claim 1, wherein each induction coil further comprises a magnetic core having a magnetic permeability substantially greater than one.

36. A plasma chamber according to claim 1, further comprising:

a center induction coil connected to the power supply and having an axial end positioned adjacent the center of the geometric surface, the center coil being surrounded by the first plurality of coils.

37. A plasma chamber according to claim 1, further comprising:

a second plurality of induction coils, wherein

each coil of the second plurality has an axial end positioned adjacent a generally planar, annular surface which is concentric with and encircles the first geometric surface,

the coils of the second plurality are equally spaced azimuthally relative to the annular surface, and

each coil has a transverse section which is wedge-shaped so that the adjacent sides of any two adjacent coils are approximately parallel to a radius of the annular surface.

38. A plasma chamber according to claim 37, wherein any two adjacent induction coils produce respective magnetic fields of opposite polarity.

6. A plasma chamber for fabricating semiconductors, comprising:

an enclosure for sealing an interior volume so as to withstand a vacuum in said interior;

a chuck for holding a semiconductor workpiece within said interior at a generally planar, circular workpiece area having a central axis;

an RF power supply;

a plurality of induction coils connected to receive electrical power from the RF power supply so that the coils produce a magnetic field in a portion of said interior, wherein

each respective coil is wound around a respective axis which is generally parallel to said central axis,

the coils are equally spaced azimuthally around said central axis, and

each coil has a transverse section which is wedge-shaped so that, for every two adjacent coils, the respective adjacent sides of said two adjacent coils are approximately parallel to a radius of the circular workpiece area.

7. A plasma chamber according to claim 6, wherein:

each induction coil has an axial end facing the workpiece area; and

the respective axial ends of all the induction coils are positioned in a plane which is parallel to the workpiece area.

8. A plasma chamber according to claim 6, wherein the power supply is connected to supply electrical power to the respective induction coils in respective polarities such that every two adjacent induction coils produce respective magnetic fields of opposite polarity.

9. A plasma chamber according to claim 8, wherein:

each induction coil is positioned at least a distance from the workpiece area; and

the adjacent sides of every two adjacent induction coils are spaced apart by an azimuthal gap which is sufficiently small, relative to said distance, so that the strength of said magnetic field is at least ten times smaller at the workpiece position than at another position within the plasma chamber which is closer to the coils.

10. A plasma chamber for fabricating semiconductors, comprising:

an enclosure for sealing an interior volume so as to withstand a vacuum in said interior;

a plurality of induction coils arranged in a rectangular array, wherein

each coil has a longitudinal axis around which that coil is wound,

the longitudinal axis of each coil is generally perpendicular to a geometric plane,

each coil has an axial end positioned adjacent the geometric plane, and

the coils are spaced apart from each other so that the transverse gap between the respective perimeters of any two adjacent coils equals a first predetermined distance which is substantially identical for any two adjacent coils; and

an RF power supply connected to supply electrical power to the induction coils so that the coils produce a magnetic field in a portion of said interior, the RF power supply being connected to the respective induction coils in respective polarities such that any two adjacent induction coils produce respective magnetic fields of opposite polarity.

11. A chamber according to claim 10, wherein each induction coil has a circular transverse cross section.

12. A chamber according to claim 10, wherein each induction coil has a rectangular transverse cross section, and wherein adjacent sides of adjacent coils are parallel.

13. A chamber according to claim 10, further comprising:

a chuck for holding a semiconductor workpiece parallel to the geometric plane.

14. A chamber according to claim 10, further comprising:

a chuck for holding a semiconductor workpiece at a position in the chamber which is a distance from the induction coils;

wherein the first predetermined distance is sufficiently small, relative to the distance between the coils and the workpiece position, so that the strength of any magnetic field produced by the coils is at least ten times smaller at the workpiece position than at another position within the plasma chamber which is closer to the coils.

34. A plasma chamber according to claim 14, wherein:

each of the coils is wound in the same direction; and

any two adjacent coils are connected to the power supply in opposite polarities so that electrical current from the power supply flows through said two adjacent coils in opposite directions.

15. A plasma chamber for fabricating semiconductors, comprising:

an enclosure for sealing an interior volume so as to withstand a vacuum in said interior;

an RF power supply; and

a number of induction coils mounted adjacent the interior and connected to the power supply, wherein

each coil has first and second ends which are respectively closer to and farther from the interior, and

each coil is connected to the power supply so that the first end of said coil is at a substantially lower RF voltage relative to electrical ground than the second end of said coil.

16. A plasma chamber according to claim 15, wherein:

the RF power supply comprises two outputs which are respectively electrically grounded and ungrounded;

the first end of each coil is connected to electrical ground; and

the second end of each coil is connected to the ungrounded power supply output.

17. A plasma chamber according to claim 15, further comprising:

a capacitor having two terminals, one of the two capacitor terminals being connected to electrical ground, and the other one of the capacitor terminals being ungrounded;

wherein the RF power supply comprises two outputs which are respectively electrically grounded and ungrounded;

wherein the induction coils are connected together in pairs such that each pair consists of two of the induction coils, and such that, for each pair of induction coils

the respective first coil ends of the two coils of the pair are connected together,

the second coil end of a first one of the coils of the pair is connected to the ungrounded terminal of the capacitor, and

the second coil end of the other one of the coils of the pair is connected to the ungrounded output of the RF power supply; and

wherein the capacitor has a capacitance value which resonates at the frequency of the RF power supply with the inductance which would be provided by connecting in parallel the respective first coils of all the coil pairs.

18. A plasma chamber according to claim 15, further comprising:

a capacitor having two terminals, one of the two capacitor terminals being connected to electrical ground, and the other one of the capacitor terminals being ungrounded;

wherein the RF power supply comprises two outputs which are respectively electrically grounded and ungrounded;

wherein the number of said induction coils is an integer N multiplied by two;

wherein the induction coils are connected together in N pairs such that each pair consists of two of the induction coils, and such that, for each pair of induction coils

the respective first coil ends of the two coils of the pair are connected together,

the second coil end of a first one of the coils of the pair is connected to the ungrounded terminal of the capacitor, and

the second coil end of the other one of the coils of the pair is connected to the ungrounded output of the RF power supply; and

wherein the capacitor has a capacitance value approximately equal to the integer N multiplied by the capacitance value which would resonate at the frequency of the RF power supply with the inductance of the first coil of one of the N coil pairs.

19. A plasma chamber according to claim 15, wherein:

the RF power supply comprises two outputs which are balanced relative to electrical ground; and

the induction coils are connected together in pairs such that each pair consists of two of the induction coils, and such that, for each pair of induction coils

the respective first coil ends of the two coils of the pair are connected together, and

the respective second coil ends of the two coils of the pair are connected to the first and second power supply outputs, respectively.

20. A plasma chamber according to claim 15, wherein:

the RF power supply comprises two outputs which are floating relative to electrical ground; and

the induction coils are connected together in pairs such that each pair consists of two of the induction coils, and such that, for each pair of induction coils

the respective first coil ends of the two coils of the pair are connected together, and

the respective second coil ends of the two coils of the pair are connected to the first and second power supply outputs, respectively.

21. A plasma source for inductively coupling electrical power to a plasma in a vacuum chamber, comprising:

a first plurality of induction coils, wherein

each coil has an axial end positioned adjacent a first geometric surface having a circular transverse section,

the coils are equally spaced azimuthally relative to said circular transverse section of the first geometric surface, and

each coil has a transverse section which is wedge-shaped so that the adjacent sides of any two adjacent coils are approximately parallel to a radius of the circular transverse section of the first geometric surface.

22. A plasma source according to claim 21, wherein:

each coil has a longitudinal axis around which that coil is wound; and

the longitudinal axis of each coil is generally perpendicular to the first geometric surface.

23. A plasma source according to claim 21, wherein any two adjacent coils produce respective magnetic fields of opposite polarity.

24. A plasma source according to claim 21 further comprising:

an electrical power supply connected to supply electrical power to the respective induction coils in respective polarities such that any two adjacent coils produce respective magnetic fields of opposite polarity.

25. A plasma source according to claim 24, wherein:

for any two adjacent coils, one of said two adjacent coils is wound clockwise, and the other one of said two adjacent coils is wound counterclockwise.

26. A plasma source according to claim 24, wherein:

each of the coils is wound in the same direction; and

any two adjacent coils are connected to the power supply in opposite polarities so that electrical current from the power supply flows through said two adjacent coils in opposite directions.

27. A plasma source according to claim 21, wherein each induction coil further comprises a magnetic core having a magnetic permeability substantially greater than one.

28. A plasma source according to claim 21, further comprising:

a center induction coil having an axial end positioned adjacent the center of the first geometric surface, the center coil being surrounded by the first plurality of coils.

29. A plasma source according to claim 21, further comprising:

a second plurality of induction coils, wherein

each coil of the second plurality has an axial end positioned adjacent a generally planar, annular surface which is concentric with and encircles the first geometric surface,

the coils of the second plurality are equally spaced azimuthally relative to the annular surface, and

each coil has a transverse section which is wedge-shaped so that the adjacent sides of any two adjacent coils are approximately parallel to a radius of the annular surface.

30. A plasma source according to claim 29, wherein any two adjacent coils produce respective magnetic fields of opposite polarity.

39. A plasma chamber according to claim 26, wherein:

for every two adjacent coils, one of said two adjacent coils is wound clockwise, and the other one of said two adjacent coils is wound counterclockwise.

40. A plasma chamber according to claim 26, wherein:

each of the coils is wound in the same direction; and

every two adjacent coils are connected to the power supply in opposite polarities so that electrical current from the power supply flows through the respective two adjacent coils in opposite directions.

41. A plasma chamber according to claim 24, wherein each induction coil further comprises a magnetic core having a magnetic permeability substantially greater than one.

42. A plasma chamber according to claim 24, further comprising:

a center induction coil which is connected to the power supply and which is wound around an axis coincident with said central axis.