Inductive plasma source with high coupling efficiency
View Patent ↗A method and apparatus are provided for processing a substrate with a radiofrequency inductive plasma in the manufacture of a device. The inductive plasma is maintained with an inductive plasma applicator having one or more inductive coupling elements. There are thin windows between the inductive coupling elements and the interior of the processing chamber. Various embodiments have magnetic flux concentrators in the inductive coupling element and feed gas holes interspersed among the inductive coupling elements. The thin windows, magnetic flux concentrators, and interspersed feed gas holes are useful to effectuate uniform processing, high power transfer efficiency, and a high degree of coupling between the applicator and plasma. In some embodiments, capacitive current is suppressed using balanced voltage to power an inductive coupling element.
1. An apparatus for processing a substrate using an inductive plasma, the apparatus comprising:
a processing chamber having an interior operable to confine a process gas;
a substrate holder in the interior of the processing chamber operable to hold a substrate;
a plurality of dielectric windows disposed on a ceiling of the chamber, each of the plurality of dielectric windows having a transverse dimension that is smaller than a span of the chamber,
an inductive plasma applicator disposed external to the chamber, the inductive plasma applicator comprising a plurality of inductive coupling elements, each of the plurality of inductive coupling elements adjacent to one of the plurality of dielectric windows;
wherein each of the plurality of inductive coupling elements includes a flat coil and a U-shaped magnetic flux concentrator of ferromagnetic material, the U-shaped magnetic flux concentrator positioned over an entire lateral width of the flat coil and across the transverse dimension of the dielectric window, the U-shaped magnetic flux concentrator having an open side facing the processing chamber interior, the U-shaped magnetic flux concentrator having a pair of legs, each of the pair of legs extending toward the chamber interior and positioned adjacent to the dielectric window, the magnetic flux concentrator operable to focus magnetic flux into the process chamber interior in a localized region proximate the dielectric window associated with the inductive coupling element such that a majority of the magnetic flux within the processing chamber from the inductive coupling element is localized in a volume between the dielectric window and the substrate and bounded by the lateral width of the associated flux concentrator.
2. The apparatus of claim 1 , wherein the plurality of dielectric windows each have a thickness of 5 mm or less.
3. The apparatus of claim 1 , wherein each pair of legs extend to within 5 mm of the processing chamber interior or less.
4. The apparatus of claim 1 , wherein at least a portion of the substrate is within approximately 5 inches of one of the plurality of inductive coupling elements.
5. The apparatus of claim 1 , wherein at least a portion of the substrate is within approximately 2 inches of one of the plurality of inductive coupling elements.
6. The apparatus of claim 1 , wherein the apparatus comprises a plurality of feed gas holes interspersed among the plurality of dielectric windows.
7. The apparatus of claim 1 , wherein the ceiling of the chamber-comprises a conductive material.
8. The apparatus of claim 7 , wherein the conductive material comprises one or more of stainless steel, a nickel molybdenum alloy, aluminum, or titanium.
9. The apparatus of claim 7 , wherein the ceiling has sufficient mechanical strength to sustain one atmosphere pressure.
10. The apparatus of claim 1 , wherein each of the plurality of thin dielectric windows is planar.
11. The apparatus of claim 7 , wherein the chamber has a diameter of approximately 0.5 meters.