AVS 51st International Symposium
    Plasma Science and Technology Tuesday Sessions
       Session PS1-TuM

Paper PS1-TuM3
Effect of Non-sinusoidal Bias Voltage Waveforms on Ion Energy Distributions and SiO@sub 2@/Si Etch Selectivity in Fluorocarbon Plasmas@footnote 1@

Tuesday, November 16, 2004, 9:00 am, Room 213A

Session: Dielectric Etching
Presenter: A. Agarwal, University of Illinois at Urbana-Champaign
Authors: A. Agarwal, University of Illinois at Urbana-Champaign
M.J. Kushner, University of Illinois at Urbana-Champaign
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During plasma etching, ion energy distributions are typically coarsely controlled by varying the amplitude of a rf sinusoidal bias voltage and/or controlling the dc bias. The resulting ion energy distribution (IED) is often broad compared to the differences between threshold energies of surface processes. Controlling the width of the IED can potentially help maintain critical dimensions of features and improve selectivity. In high-plasma density, low gas pressure systems, sheaths are typically collisionless and so additional control over IEDs can be obtained by controlling the sheath voltage. In this regard, non-sinusoidal bias waveforms have been proposed as a means to tailor the IEDs.@footnote 2@,@footnote 3@ In this talk, we report on results from a computational investigation of IED control by using a tailored non-sinusoidal bias voltage waveform. A 2-dimensional plasma equipment model has been linked with a Monte Carlo feature profile model to assess the consequences of the resulting IEDs on the selectivity of etching SiO@sub 2@ to Si in fluorocarbon ICP plasmas and capacitively coupled plasmas. The most stringent control over the IEDs is obtained at lower frequencies where sheath crossing times are short compared to the rf period and in gas mixtures where the masses of the ions are similar. Slightly more collisional plasmas (provided the sheath remains collisionless) also provide more stringent control by reducing the energy of ions entering the sheath proper. @FootnoteText@ @footnote 1@ Work supported by SRC and NSF. @footnote 2@ S. B. Wang and A. E. Wendt, J. Vac. Sci. Technol. A, 19, 2425 (2001) @footnote 3@ S. Rauf, J. Appl. Phys., 87, 7647 (2000).