Symmetrical inductively coupled plasma source with coaxial RF feed and coaxial shielding
A plasma reactor has an overhead multiple coil inductive plasma source with symmetric RF feeds and symmetrical RF shielding around the symmetric RF feeds.
1. A plasma reactor comprising:
a window assembly;
concentric inner and outer coil antennas adjacent said window assembly;
inner and outer current distributors each comprising an inverted bowl-shaped conductor coupled to said inner and outer coil antennas, respectively, and wherein said outer current distributor concentrically surrounds said inner current distributor, and wherein each inverted bowl-shaped conductor comprises an axially symmetric hollow body comprising a bottom edge facing and terminated at a supply end of the corresponding one of said inner and outer coil antennas;
a ceiling plate overlying said window assembly and first and second RF power terminals at said ceiling plate;
a plenum plate between said ceiling plate and said inner and outer current distributors, the plenum plate comprising a central opening, the central opening being coaxial with said inner and outer coil antennas;
first and second axial RF power feeds connected at respective connections between respective ones of said first and second RF power terminals and respective ones of said inner and outer current distributors, wherein said first axial RF power feed coincides with an axis of symmetry of said coil antennas, the respective connection corresponding to said inner current distributor being located on said axis of symmetry, and wherein said second axial RF power feed extends downwardly through said central opening with a gap between said plenum plate and said second axial RF power feed, and said second axial RF power feed includes outwardly extending portions that project past an edge of said central opening and axially extending portions projecting downward from the outwardly extending portions to contact a top of the inverted bowl-shaped conductor of said outer current distributor.
2. The plasma reactor of claim 1 wherein said first axial RF power feed comprises a center RF connection rod, and wherein said center RF connection rod and said outer current distributor are coaxial.
3. The plasma reactor of claim 2 wherein said inner and outer coil antennas are coaxial with said center RF connection rod.
4. The plasma reactor of claim 2 , wherein said second axial RF power feed comprises a distribution cylinder surrounding said center RF connection rod.
5. The plasma reactor of claim 4 further comprising plural spaced-apart reactance elements coupled to said distribution cylinder.
6. The plasma reactor of claim 5 wherein said reactance elements comprise discrete capacitors coupled between said distribution cylinder and said ceiling plate.
7. The plasma reactor of claim 4 , wherein the outwardly extending portions extend from a bottom edge of said distribution cylinder.
8. The plasma reactor of claim 1 wherein the outwardly extending portions comprise a radial flange overlying said gap.
9. The plasma reactor of claim 1 wherein the outwardly extending portions comprise plural radial outer arms.
10. The plasma reactor of claim 1 , comprising plural axial outer legs that connect the outwardly extending portions to said outer current distributor.
11. The plasma reactor of claim 10 , comprising a ground plate between said plenum plate and said outer coil antenna.
12. The plasma reactor of claim 11 , wherein said plural axial outer legs extend through said ground plate.
13. The plasma reactor of claim 1 wherein said outer coil antenna comprises a cylindrical side coil and wherein said window assembly comprises a disk-shaped window facing said inner coil antenna and a cylindrical side window facing said cylindrical side coil.