Apparatus and method for electrostatically shielding an inductively coupled RF plasma source and facilitating ignition of a plasma

• US 6,248,251 B1
• Filed: 02/19/1999
• Issued: 06/19/2001
• Est. Priority Date: 02/19/1999
• Status: Expired due to Term

• Current Assignee: Tokyo Electron Limited
• Original Assignee: Tokyo Electron Limited
• Inventors: Sill, Edward L.
• Primary Examiner(s): MCDONALD, RODNEY GLENN
• Application Number:
  US09/255,613
• Time in Patent Office: 851 Days
• Field of Search: 118/723.AN, 118/723.I, 118/723.IR, 156/345, 204/298.31, 204/298.34, 204/298.37, 204/192.32, 216/67, 216/68, 427/569
• US Class Current: 216/68
• CPC Class Codes: H01J 37/32009 Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources plasma generation in general H05H1/24
• CPC Class Codes: H01J 37/321 the radio frequency energy being inductively coupled to the plasma

Abstract

A plasma etch apparatus (10) such as that for etching wafers in the manufacture of semiconductors includes a vacuum chamber (15) surrounded by a cylindrical dielectric wall (13). A coil (20) surrounds the chamber outside of the wall and is energized with medium frequency RF energy which is inductively coupled into the chamber to energize a plasma in the chamber to etch a semiconductor wafer (16) on a support (17) in the chamber. A generally cylindrical Faraday shield (30) surrounds the outside of the chamber in contact with the outside of the wall between the wall and the coil. The shield has a plurality of axially oriented slits (32) therein closely spaced around the shield and extending less than the height of the shield. One slit or gap (31) extends the full height of the shield and interrupts an otherwise continuous conductive path around the circumference of the chamber. The gap is about ⅛ inch wide, so that, upon initial energization of the coil, a momentary peak-to-peak RF voltage forms across the gap, which generates an electric field in the chamber in the vicinity of the gap which ignites the plasma.

Claims

1. An apparatus for plasma processing a substrate comprising:

a vacuum chamber having a dielectric wall;

an inductor positioned outside of the chamber in proximity to the wall;

an RF energy source connected to the inductor;

a Faraday shield positioned between the inductor and the wall, the shield being in the shape of a loop having opposite ends and a circumference interrupted by at a full height gap that interrupts the entire height of the shield and is bordered by the opposite ends of the shield, whereby the opposite ends of the shield are in close proximity to each other across the gap;

the shield having a localized ground connection that allows RF current induced around the loop to develop a peak-to-peak voltage across the opposite ends of the loop and the gap that is sufficiently high, when no RF plasma is present in the chamber, to produce a plasma igniting electric field adjacent the gap inside of the wall of the chamber.

2. The apparatus of claim 1 wherein:

the gap is between approximately {fraction (1/16)} and ⅛

inch wide.

3. The apparatus of claim 2 wherein:

the gap is approximately ⅛

inch wide.

4. The apparatus of claim 1 wherein:

the shield is in contact with the outside of the dielectric chamber wall.

5. The apparatus of claim 1 wherein:

the wall of the chamber is cylindrical and defines an axis of symmetry;

the inductor is a helical coil surrounding the cylindrical chamber wall; and

the shield is cylindrical and has a height at least as great as that of the coil with the gap extending the height of the shield and disposed substantially parallel to the axis of symmetry of the cylindrical chamber wall.

6. The apparatus of claim 5 wherein:

the shield has a plurality of circumferentially-spaced slots therein extending only partially the height of the shield which are disposed generally parallel to the axis of symmetry of the cylindrical chamber wall.

7. The apparatus of claim 1 wherein:

the shield has a plurality of transverse slots therein spaced along the circumference of the shield, each slot extending partially across the loop.

8. The apparatus of claim 1 wherein:

the localized ground connection is located at one section of the circumference of the loop approximately midway between the opposite ends.

9. A plasma etching apparatus comprising:

a vacuum chamber having and axis and a dielectric side wall surrounding the axis;

a coil outside of the chamber and surrounding the dielectric side wall;

an RF energy source connected across the coil;

an electrically conductive Faraday shield extending in a loop circumferentially around the outside of the chamber adjacent the outside of the side wall between the coil and the side wall, the shield having a full height gap that interrupts the entire height of the shield and is bordered by opposite ends of the shield and being grounded along a limited portion of its circumference such that RF current induced around the loop develops a peak-to-peak voltage across the loop that is sufficiently high to produce a plasma igniting electric field in the vicinity of the gap inside of the wall of the chamber.

10. The apparatus of claim 9 wherein:

the gap is between approximately {fraction (1/16)} and ⅛

inch wide.

11. The apparatus of claim 9 wherein:

the shield is in contact with the outside of the chamber wall.

12. The apparatus of claim 9 wherein:

the wall of the chamber is cylindrical and defines an axis of symmetry;

the inductor is a helical coil surrounding the cylindrical chamber wall; and

the shield is cylindrical and has a height at least as great as that of the coil with the gap being an axial gap extending the height of the shield.

13. The apparatus of claim 12 wherein:

the shield has a plurality of spaced axial slots therein extending only partially the height of the shield.

14. The apparatus of claim 9 wherein:

the shield has a plurality of axial slots therein extending partially across the loop and spaced along the circumference of the shield.

15. The apparatus of claim 9 wherein:

the shield has a ground connection located at one section of the circumference of the loop approximately midway between the ends.

16. A method of electrostatically shielding an inductively coupled RF plasma source and igniting a plasma in a vacuum processing chamber, the method comprising the steps of:

providing an inductor outside of the wall of a processing chamber in a position to inductively couple RF energy into a plasma in the chamber when energized therewith;

providing a shield between the inductor and the wall in a loop substantially encircling the chamber wall that is interrupted by at least one full height gap that interrupts the entire height of the shield;

grounding the shield at only a selected limited portion of the loop so as to allow a peak-to-peak RF voltage to develop in the shield across the gap; and

igniting a plasma in the chamber by energizing the inductor with an RF energy to induce RF current momentarily in the shield and produce a peak-to-peak voltage across the gap of the shield to produce an electric field inside the wall of the chamber in the vicinity of the gap to ignite the plasma in the chamber.

17. The method of claim 16 wherein:

the inductor providing step includes the step of providing a helical coil outside of the wall and surrounding the processing chamber;

the shield providing step includes the step of providing a cylindrical shield located between the coil and the wall in contact with the wall; and

the at least one gap is a gap extending along one side of the chamber.

18. The method of claim 16 wherein:

the shield providing step includes the step of providing a shield having a gap that is between approximately {fraction (1/16)} and ¼

inches in width.

19. The method of claim 16 wherein:

the shield providing step includes the step of providing a shield having a plurality of spaced slits therein extending almost, but less than, entirely across the shield, the slits being approximately as wide as the gap and having spacings between the slits about as wide as the gap.

20. The method of claim 16, further comprising the steps of:

providing a wafer in the chamber and sealing the chamber before energizing the inductor; and

following ignition of the plasma, continuing to energize the plasma with energy inductively coupled from the inductor, electrically attracting ions from the plasma onto the surface of the wafer and etching the wafer therewith.

21. An apparatus for plasma processing a substrate comprising:

a vacuum chamber having a dielectric wall;

an inductor positioned outside of the chamber in proximity to the wall;

an RF energy source connected to the inductor;

a Faraday shield positioned between the inductor and the wall, the shield being made of electrically conductive material and formed in the shape of at least one loop having at least one full height gap therein that interrupts the entire height of the shield and is oriented to interrupt the path of current induced therein by RF energy coupled by the coil from the source, the at least one gap defining opposed ends of the material in sufficiently close proximity to each other across the at least one gap to produce a temporary peak-to-peak voltage across said opposite ends that is sufficiently high adjacent the gap, on the opposite side of the wall therefrom, inside of the chamber, to produce an electric field that is effective to ignite a plasma inside of the chamber.

22. The apparatus of claim 21 wherein:

the at least one gap is a single gap completely interrupting the circumference of the shield.

23. The apparatus of claim 21 wherein:

the shield has a localized ground connection so as to provide effective shielding of capacitive coupling of voltage from the coil to the plasma within the chamber.

24. The apparatus of claim 21 wherein:

the shield has a plurality of slits therein effective to allow inductive coupling of the RF energy into the chamber.

25. The apparatus of claim 21 wherein:

the shield has a ground connection that is localized to a limited section of the inductor so as to allow a peak-to-peak voltage to develop across the gap when the RF current is initially induced into the shield from the inductor.

26. The apparatus of claim 21 wherein:

the temporary peak-to-peak voltage is at least several thousand volts.

27. The apparatus of claim 21 wherein:

the temporary peak-to-peak voltage is approximately 5000 volts.