Low density high frequency process for a parallel-plate electrode plasma reactor having an inductive antenna

• US 6,036,878 A
• Filed: 02/13/1998
• Issued: 03/14/2000
• Est. Priority Date: 02/02/1996
• Status: Expired due to Term

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Collins, Kenneth
• Primary Examiner(s): DANG, THI D
• Application Number:
  US09/023,365
• Time in Patent Office: 760 Days
• Field of Search: 216/68, 438/729
• US Class Current: 216/68
• CPC Class Codes: H01J 37/321 the radio frequency energy being inductively coupled to the plasma
• CPC Class Codes: H01J 37/32165 Plural frequencies
• CPC Class Codes: H01J 37/32458 Vessel
• CPC Class Codes: H01J 37/32467 Material
• CPC Class Codes: H01J 37/32522 Temperature
• CPC Class Codes: H01L 21/6831 using electrostatic chucks

Abstract

The present invention is embodied in a method of operating an inductively coupled plasma reactor for processing a semiconductor wafer, the reactor including a vacuum chamber for containing the wafer, a process gas source, a semiconductor window electrode facing an interior portion of the chamber, an inductive power radiator on an exterior side of the semiconductor window electrode, the inductive field having a skin depth generally decreasing with the frequency of the RF inductive field and with the density of the plasma in the chamber and generally increasing with the pressure inside the vacuum chamber, the inductive coupling of the RF field tending to approach extinguishment as the skin depth approaches the spacing between the wafer and the window electrode, a method for maintaining an intermediate plasma density inside the chamber without extinguishing the inductive coupling of the RF field, the method including operating the reactor at a selected flow rate of the process gas, a selected chamber pressure and a selected plasma source power level corresponding to the reduced plasma density, and maintaining the frequency of the RF field at least at a level sufficient to limit the skin depth to a depth less than the electrode-to-wafer spacing, whereby to maintain the inductive coupling of the RF field.

Claims

1. In an inductively coupled plasma reactor for processing a semiconductor wafer, the reactor comprising a vacuum chamber for containing said wafer, a process gas source, a semiconductor window electrode facing an interior portion of said chamber, an inductive power radiator on an exterior side of said semiconductor window electrode, said RF field having a skin depth generally decreasing with the frequency of said RF field and with the density of the plasma in said chamber and generally increasing with the pressure inside said vacuum chamber, the inductive coupling of said RF field tending to approach extinguishment as said skin depth approaches the spacing between said wafer and said window electrode, a method for maintaining an intermediate plasma density inside said chamber less than a high plasma density without extinguishing said inductive coupling of said RF field, said method comprising:

operating said reactor at a selected flow rate of said process gas, a selected chamber pressure and a selected plasma source power level corresponding to said intermediate plasma density;

maintaining the frequency of said RF field at least at a level sufficient to limit said skin depth to a depth less than the electrode-to-wafer spacing, whereby to maintain said inductive coupling of said RF field.

2. The method of claim 1 wherein said electrode-to-wafer spacing in on the order of about 7 cm.

3. The method of claim 1 wherein said high plasma density is between about 1·

10¹¹ electrons/cm³ to 10·

10¹¹ electrons/cm³ and said intermediate plasma density is between about 1·

10¹⁰ electrons/cm³ to 10·

10¹⁰ electrons/cm³.

4. The method of claim 1 wherein said frequency exceeds, by a factor of between 4 and 100, frequencies at which a high plasma density is obtained.

5. The method of claim 1 wherein said frequency is on the order of about 13 MHz.

6. The method of claim 1 wherein said frequency is on the order of between about 13 and 100 MHz.

7. The method of claim 1 wherein said chamber pressure lies in a range between on the order of about 2 mTorr and 100 mTorr.

8. The method of claim 1 wherein said chamber pressure lies in a range between on the order of about 2 mTorr and 200 mTorr.

9. The method of claim 1 wherein said process gas comprises etchant and polymer precursor gases.

10. The method of claim 4 wherein said factor is on the order of between about 6 and 7.

11. The method of claim 3 wherein said chamber pressure is in a range of between about 25 to 100 mTorr.

12. The method of claim 3 wherein said chamber pressure is in a range of between about 40 and 100 mTorr.

13. The method of claim 3 wherein said chamber pressure is in a range of between about 2 and 25 mTorr.

14. The method of claim 3 wherein said chamber pressure is in a range of between about 2 and 40 mTorr.

15. The method of claim 4 wherein said intermediate plasma density is within about one order of magnitude of a high plasma density.

16. The method of claim 15 wherein said electrode-to-wafer spacing is a fraction of the diameter of said wafer.

17. The method of claim 1 wherein said reactor further comprises an RF bias power generator for applying plasma bias power to said wafer, said method further comprising:

maintaining the frequency of said RF bias power generator at least at a level sufficient to limit ion energies near said wafer below a desired threshold.

18. The method of claim 17 wherein said bias power frequency is maintained above 10 MHz.