AVS 45th International Symposium
    Plasma Science and Technology Division Thursday Sessions
       Session PS-ThA

Paper PS-ThA6
Multi-Frequency Operation of RIE and ICP Sources@footnote 1@

Thursday, November 5, 1998, 3:40 pm, Room 318/319/320

Session: Diagnostics II
Presenter: S. Rauf, University of Illinois, Urbana-Champaign
Authors: S. Rauf, University of Illinois, Urbana-Champaign
M.J. Kushner, University of Illinois, Urbana-Champaign
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In both inductively and capacitively coupled rf discharges, the source frequency strongly influences the plasma and electrical properties. Multiple sources at different frequencies are often simultaneously used to combine their attractive features. For example, the goal of dual-frequency RIE plasmas is to separately optimize the magnitude and energy of ion fluxes to the substrate. If the source frequencies are significantly different from each other, the resulting plasma properties can generally be characterized in terms of the separate contributions of the individual sources. However, when the frequencies are close to each other (e.g., 6.78 MHz and 13.56 MHz), the sources interact through the nonlinear plasma medium, thereby complicating this additive relationship. The dynamics of rf plasma processing reactors with multi-frequency sources have been investigated using a coupled plasma equipment-circuit model. In capacitively coupled Ar and Ar/CF@sub 4@ discharges, the addition of a high frequency source (27.12 MHz) on the opposing electrode decreases the magnitude of the dc bias at the substrate (13.56 MHz) due to nonlinear interaction between the separately powered sheaths and a reapportionment of current. In ICP reactors, the dc bias on the substrate has a strong dependence on the rf bias frequency (becoming more negative at higher frequencies) due to the differences in sheath impedance at the powered substrate and the grounded walls. This relationship can be altered by repositioning the antenna which, in turn, reapportions the current collected on biased and grounded surfaces. It was also found that by adding rf sources at remote locations from the substrate in ICP reactors, such as small areas of the wall, one can control the dc bias at the substrate without appreciably changing the ion flux or electron temperature. @FootnoteText@ @footnote 1@Work supported by AFOSR/DARPA, SRC and NSF.