AVS 51st International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS-WeA

Paper PS-WeA6
Measurements and Consequences of Non-Uniform RF Plasma Potential due to Surface Asymmetry in Large Area RF Capacitive Reactors

Wednesday, November 17, 2004, 3:40 pm, Room 213A

Session: Plasma Diagnostics
Presenter: L. Sansonnens, Ecole Polytechnique Fédérale de Lausanne, Switzerland
Authors: L. Sansonnens, Ecole Polytechnique Fédérale de Lausanne, Switzerland
L. Derendinger, Ecole Polytechnique Fédérale de Lausanne, Switzerland
C. Hollenstein, Ecole Polytechnique Fédérale de Lausanne, Switzerland
A.A. Howling, Ecole Polytechnique Fédérale de Lausanne, Switzerland
H. Schmidt, Ecole Polytechnique Fédérale de Lausanne, Switzerland
J.P.M. Schmitt, UNAXIS-France SA, France
E. Sakanaka, UNAXIS-France SA, France
Correspondent: Click to Email
In small area capacitive reactors, the RF and DC plasma potential can be assumed to be uniform over the reactor area, and asymmetry between the grounded and powered electrodes leads to the well-known area law for determining the uniform DC and RF voltage amplitude across both plasma sheaths. In large area reactors, however, the RF plasma potential can vary over a long range across the reactor area due to the finite plasma conductivity. A local asymmetry of electrode area due, for example, to the lateral grounded walls for plasma confinement, causes a local RF plasma potential perturbation which propagates along the resistive plasma between capacitive sheaths. This propagation can be described by a telegraph equation for which a typical damping length can be determined. In this way, for a non-symmetric reactor wider than the damping length, the RF sheath voltage amplitudes which are unequal close to the reactor edges tend to be the same in the centre as for a symmetric reactor. A predicted consequence of this non-uniform RF plasma potential is the presence of non-ambipolar current circulating through the plasma and along conducting electrodes. In this work, we present measurements of the RF plasma potential and DC net current distribution over the grounded electrode of a large area reactor (57 x 47 cm@super 2@) using an array of surface probes, for various reactor geometry configurations. These experimental results are compared with a two-dimensional solution of the telegraph propagation model. Finally, we present some effects of the non-uniform RF plasma potential such as non-uniform power dissipation in the plasma which have important consequences for plasma processing.