Decay Processes of Electrons in the Afterglow of High-Density CF_4, c-C_4F_8 and CF_4-H_2 Plasmas

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Temporal variation of electron density was measured using a conventional microwave interferometer in the afterglow of high-density CF_4, c-C_4F_8 and CF_4 -H_2 plasmas. In most experimental conditions, the electron loss frequency ν_e evaluated from the temporal variation of electron density n_e such that ν_e = -(dn_e/dt)/n_e corresponds to the frequency of dissociative electron attachment to neutral molecules. Since negative fluorine ions (F^-) are produced by dissociative electron attachment, the production efficiency of F^- in various plasmas can be investigated simply by the observation of ν_e. In the CF_4 plasma, the variation of the electron loss frequency roughly agreed with that of CF_x radical densities. In the C_4F_8 plasma, the electron loss frequency was higher for a discharge condition with a lower degree of dissociation. These results indicate that reaction products play important roles in the production of F^- in the CF_4 plasma, while in the C_4F_8 plasma, the production of F^- is dominated by the parent gas (C_4F_8) and relatively heavy molecules C_xF_y (x ≥ 2) produced in the plasmas. The results observed in the CF_4 -H_2 plasma suggest that the density of F_2 is not high enough to dominate the production of F^-.
社団法人応用物理学会の論文
1999-07-30