Properties of Inductively Coupled Radio Frequency CH4/H2 Plasmas: Experiments and Global Model

概要

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Experiments with a Langmuir probe and optical emission spectroscopy combined with actinometry are carried out in inductively coupled rf (13.56 MHz) CH4/H2 plasmas at three total pressures of 25, 50, and 100 mTorr for hydrogen fractions ranging from 0 to 80%. The measured electron density gradually decreases with increasing hydrogen fraction, whereas the measured effective electron temperature slightly increases with hydrogen fraction. The density of hydrogen atoms estimated by actinometry does not strongly depend on hydrogen fraction. The high density of hydrogen molecules can be expected even in CH4 plasmas from the optical intensity emitted from the excited hydrogen molecules. A global model is analyzed in order to understand the plasma chemistry in CH4/H2 plasmas. In the model, the dominant neutral species are always hydrogen and CH4 molecules, followed by hydrogen atoms and hydrocarbons, such as C2Hn (n=1, 2, and 4). On the other hand, the dominant ions are CH5+, C2H+, C2H3+, C2H5+, and C3H5+ at low hydrogen fraction, whereas H3+ ions become dominant ion species as hydrogen fraction increases.
2012-04-25