A VOLTAGE UNIFORMITY STUDY IN LARGE-AREA REACTORS FOR RF PLASMA DEPOSITION

Non-uniform voltage distribution across the electrode area results in inhomogeneous thin-film RF plasma deposition in large-area reactors. I n this work, a two-dimensional analytic model for the calculation of t he voltage distribution across the electrode area is presented. The re sults of this model are in good agreement with measurements performed without plasma at 13.56 MHz and 70 MHz in a large-area reactor. The pr incipal voltage inhomogeneities are caused by logarithmic singularitie s in the vicinity of RF connections and not by standing waves. These s ingularities are only described by a two-dimensional model and cannot be intuitively predicted by analogy to a one-dimensional case. Plasma light emission measurements and thickness homogeneity studies of a-Si: H deposited films show that the plasma reproduces these voltage inhomo geneities. Improvement of the voltage uniformity is investigated by ch anging the number and position of the RF connections.