Plasma reactor vessel having improved plasma uniformity comprised of a first electrode, a second electrode opposed to the first electrode, and a third electrode between a substrate carrier and the second electrode
Plasma reactor vessel comprising a vacuum chamber; a first electrode in the vacuum chamber; a second electrode in the vacuum chamber, opposed to the first electrode and spaced from the first electrode; a power source electrically connected to one of the first or second electrodes; a substrate carrier having an electrically conductive material, the substrate carrier being configured to be in electrical contact with the second electrode and to hold a substrate at such that at least the majority of upper and lower surfaces of the substrate are untouched by any part of the plasma reactor and can be exposed to the plasma. The reactor vessel further includes a third electrode between the substrate carrier and the second electrode, wherein the third electrode is electrically insulated from the second electrode. And the third electrode and the substrate carrier are arranged such that when the substrate carrier holds a substrate, a first clearance gap is between the substrate and the third electrode. There is further provided a corresponding assembly and method for performing plasma processing.
1. Plasma reactor vessel, comprising
a vacuum chamber;
a first electrode in the vacuum chamber;
a second electrode in the vacuum chamber, opposed to the first electrode and spaced from the first electrode;
a means for providing reactive process gases in the vacuum chamber;
a power source electrically connected to one of the first or second electrodes, for applying a main RF voltage to one of the first and second electrodes, the other electrode being grounded;
a substrate carrier comprising an electrically conductive material, the substrate carrier being configured to be in electrical contact with the second electrode and to hold a substrate such that at least the majority of upper and lower surfaces of the substrate are untouched by any part of the plasma reactor and can be exposed to the plasma;
the reactor vessel further comprising a third electrode beneath the substrate carrier and between the substrate carrier and the second electrode, wherein the third electrode is electrically insulated from said second electrode; and
wherein the third electrode and the substrate carrier are arranged such that, when the substrate carrier holds a substrate, a first clearance gap is comprised between the substrate and the third electrode.
2. Plasma reactor vessel according to claim 1 further comprising a compensating device configured to provide a compensating RF voltage to the third electrode, the compensation RF voltage having a modulation phase opposite to the modulation phase of the RF voltage differential between the first electrode and the second electrode.
3. The reactor according to claim 2 , wherein the first clearance gap between the third electrode and substrate is between 0.5 mm and 3 mm.
4. The reactor according to claim 1 ,
further comprising a second clearance gap beneath the third electrode and between the third electrode and said second electrode, the second clearance gap electrically insulating the third electrode from said second electrodes.
5. The reactor according to claim 2 ,
wherein said compensating device comprises a voltage source which can generate an RF signal, and the third electrode is electrically connected to the voltage source via a feed line.
6. The reactor according to claim 2 ,
wherein said compensating device comprises a coiled self-inductance electrically connecting said second electrode to the third electrode.
7. The reactor according to claim 1 ,
further comprising insulating spacing elements between the third electrode and said second electrode, the magnitude of the second clearance gap being determined by the height of the insulating spacing elements.
8. The reactor according to claim 7 ,
wherein said insulating spacing elements comprise ceramic blocks.
9. The reactor according to claim 1 ,
wherein said substrate carrier is configured to hold a plurality of the substrates.
10. The reactor according to claim 9 ,
wherein the substrate carrier comprises a plurality of cut-out portions, each cut-out portion being adapted to receive a substrate.
11. The reactor according to claim 10 ,
the reactor vessel comprises a plurality of the third electrodes, each of said plurality of the third electrode being aligned with a corresponding cut-out portion in the substrate carrier.