Method of operating a plasma reactor having an overhead electrode with a fixed impedance match element

• US 20070251920A1
• Filed: 05/25/2007
• Published: 11/01/2007
• Est. Priority Date: 03/17/2000
• Status: Abandoned Application

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Hoffman, Daniel
• Application Number:
  US11/807,194
• Publication Number:
  US 20070251920A1
• Time in Patent Office: Days
• US Class Current: 216/67
• 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 method is provided for processing a workpiece in a plasma reactor chamber having a ceiling electrode and a workpiece support pedestal within the chamber facing the ceiling electrode and supporting the workpiece. The method includes providing a fixed impedance match element between a generator of VHF plasma source power and the ceiling electrode. The method further includes introducing a process gas into the chamber and supplying VHF plasma source power from the generator to the ceiling electrode to generate a plasma having a plasma ion density in the chamber. The reactance of the ceiling electrode is selected to establish a plasma-electrode resonant frequency of a resonance formed between the plasma and the ceiling electrode at least nearly equal to the frequency of the VHF plasma source power.

Claims

1. A method of processing a workpiece in a plasma reactor chamber having a ceiling electrode and a workpiece support pedestal within the chamber facing the ceiling electrode and supporting the workpiece, comprising:

providing a fixed impedance match element between a generator of VHF plasma source power and said ceiling electrode;

introducing a process gas into the chamber and supplying VHF plasma source power from said generator to said ceiling electrode to generate a plasma having a plasma ion density in said chamber; and

selecting the reactance of said ceiling electrode to establish a plasma-electrode resonant frequency of a resonance formed between the plasma and the ceiling electrode at least nearly equal to the frequency of said VHF plasma source power.

2. The method of claim 1 further comprising coupling RF plasma bias power of an HF or LF frequency to said workpiece through the workpiece support pedestal.

3. The method of claim 1 wherein said frequency of said VHF plasma source power is offset from said plasma-electrode resonant frequency by a fraction of said plasma-electrode resonant frequency.

4. The method of claim 3 further comprising selecting a resonant frequency of the impedance match element to be at least near or equal to said frequency of said VHF plasma source power.

5. The method of claim 4 wherein said resonant frequency of said impedance match element is offset from said frequency of the VHF plasma source power by a fraction of said frequency of said VHF plasma source power.

6. The method of claim 4 wherein said resonant frequency of said impedance match element is offset from the plasma-electrode resonant frequency by a fraction of said plasma-electrode resonant frequency.

7. The method of claim 6 further comprising selecting the frequency of VHF plasma source power to lie between said plasma-electrode resonant frequency and said resonant frequency of said match element.

8. The method of claim 1 wherein the step of providing an impedance matching element comprises connecting the generator to the impedance match element at a tap point at least near an ideal point at which a voltage-to-current standing wave ratio is equal to an output impedance of said generator.

9. The method of claim 8 further comprising offsetting said tap point from said ideal point by about 5% of a wavelength of said VHF plasma source power.

10. The method of claim 8 further comprising offsetting said tap point from said ideal location by an amount sufficient to realize an increase of 6:

1 in impedance match space.

11. The method of claim 8 further comprising offsetting said tap point from said ideal location by an amount that is sufficient to realize an addition of current at said tap point whenever the load impedance at said ceiling electrode falls below a nominal level and a subtraction of current at said tap point whenever the load impedance at said ceiling electrode exceeds the nominal level.

12. The method of claim 1 further comprising maintaining plasma ion density in said chamber between about 10⁹ per cc and 10¹² per cc.

13. A method of processing a workpiece in a plasma reactor chamber having a ceiling electrode and a workpiece support pedestal within the chamber facing the ceiling electrode and supporting the workpiece, comprising:

coupling a coaxial tuning stub to the ceiling electrode as a fixed impedance match element, said coaxial tuning stub having a stub resonant frequency;

introducing a process gas into the chamber;

applying VHF plasma source power through the coaxial tuning stub to said electrode to generate a plasma having a plasma ion density in said chamber;

selecting the reactance of said ceiling electrode to establish a plasma-electrode resonant frequency of a resonance formed between the plasma and the ceiling electrode at least nearly equal to the frequency of said VHF plasma source power; and

selecting a length of said coaxial tuning stub to provide a stub resonant frequency at least nearly equal to the frequency of said VHF source power.

14. The method of claim 13 further comprising coupling RF plasma bias power of an HF or LF frequency to said workpiece through the workpiece support pedestal.

15. The method of claim 13 wherein said frequency of said VHF plasma source power is offset from said plasma-electrode resonant frequency by a fraction of said plasma-electrode resonant frequency.

16. The method of claim 15 wherein the resonant frequency of said coaxial tuning stub is offset from the frequency of the VHF plasma source power by a fraction of the frequency of said VHF plasma source power.

17. The method of claim 16 wherein the resonant frequency of said coaxial tuning stub is offset from the plasma-electrode resonant frequency by a fraction of said plasma-electrode resonant frequency.

18. The method of claim 17 further comprising selecting the frequency of VHF plasma source power to lie between said plasma-electrode resonant frequency and said resonant frequency of said coaxial tuning stub.

19. The method of claim 13 wherein the step of applying VHF source power through the coaxial tuning stub comprises applying the VHF source power to a tap point of the coaxial tuning stub at least near an ideal point at which a voltage-to-current standing wave ratio is equal to an output impedance of said generator.

20. The method of claim 19 further comprising offsetting said tap point from said ideal point by about 5% of a wavelength of said VHF plasma source power.