AVS 65th International Symposium & Exhibition
    Plasma Science and Technology Division Thursday Sessions
       Session PS-ThM

Paper PS-ThM11
Resonant Element Microwave Plasma Source

Thursday, October 25, 2018, 11:20 am, Room 104A

Session: Plasma Sources
Presenter: Barton Lane, Tokyo Electron, America, Inc.
Authors: B. Lane, Tokyo Electron, America, Inc.
P.L.G. Ventzek, Tokyo Electron, America, Inc.
A. Bhakta, Tokyo Electron, America, Inc.
K. Nagaseki, Tokyo Electron Miyagi, Ltd.
A. Ranjan, Tokyo Technology Center America
Correspondent: Click to Email
We report here the use of resonant elements for plasma generation. The resonant elements are realized as metal structures embedded in alumina using a metal printing and lamination process. The embedded structures present a flat featureless alumina face to the plasma which is optimal for reducing particle generation. The structures are chosen to be resonant in the microwave frequency range and thus have geometric sizes of approximately 10 mm, although this can be chosen for the particular application. The structures can be viewed as LC circuits which have a number of resonances in the microwave band each with a corresponding spatial electric field eigenmode. The geometry of the structures reported here positions the inductive portion near to the plasma and in one eigenmode produces inductively generated circular mirror currents in the plasma which have a spatial dimension of 10 mm. The LC structures which we report on have a quadrupole symmetry in order to minimize the coupling to surface waves which tend to propagate away from the launch structure and are difficult to control. The fields responsible for plasma generation are the near fields of the resonant structure and these die away quickly from the structure giving a localized plasma generation region. The alumina blocks in which the resonant element structures are embedded are pierced by cylindrical holes through which gas is injected into the generated plasma. For one eigenmode of this system at low pressures ( ~ 10 mTorr) the electric fields are such that the plasma concentrates in the supersonic gas jet and has a size of approximately 1 mm. The structures can also be used to sustain a plasma in a high pressure cavity which then serves as a source of radicals through jet outlets. In this case the cavity pressures are in the several Torr or higher range. With the addition of small permanent magnets operation in the 0.1 mTorr regime is possible by exploiting the electron cyclotron phenomenon. The resonant elements can be arranged in an array. We report on a linear array which is coupled by TEM parallel plate transmission lines embedded in the alumina. Because the presence of plasma tends to detune the structures from resonance there is a natural negative feedback which helps to balance the multiple elements producing a reasonably uniform “curtain” of plasma. The ability to extend such an array to cover the entire upper electrode of a semiconductor reactor has been noted as well as the ability to control the spatial distribution by choosing different natural resonances for different regions of the reactor.