Nonlinear dynamics of radio frequency plasma processing reactors powered by multifrequency sources

The source frequency has a strong influence on plasma characteristics in RF discharges. Multiple sources at widely different frequencies are often sim ultaneously used to separately optimize the magnitude and energy of ion flu xes to the substrate. In doing so, the sources are relatively independent o f each other. These sources can, however, nonlinearly interact if the frequ encies are sufficiently close. The resulting plasma and electrical characte ristics can then be significantly different from those due to the sum of th e individual sources, In this paper, a plasma equipment model is used to in vestigate the interaction of multiple frequency sources in capacitively and inductively coupled RF excited plasmas. In capacitively coupled systems, w e confirmed that the plasma density increases with increasing frequency but also found that the magnitude of the de bias and de sheath voltage decreas es, To produce a capacitively coupled discharge having a high plasma densit y with a large de bias, we combined low and high frequency sources. The pla sma density did increase using the dual frequency system as compared to the single low frequency source, The sources, however, nonlinearly interacted at the grounded wall sheath, thereby shifting both the plasma potential and de bias, In inductively coupled plasmas (ICP), the frequency of the capaci tive substrate bias does not have a significant effect on electron temperat ure and density. The de bias and de sheath voltage at the substrate were, h owever, found to strongly depend on source frequency, By using additional R F sources at alternate locations in ICP reactors, it was found that the de bias at the substrate was varied without significantly changing other plasm a parameters, such as the substrate sheath potential.