Dilution-Gas Effect on Electron Density and Temperature in RF SiH_4 Plasma Based on Microwave Cavity Resonance Measurement

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Using a microwave cavity resonance technique, the electron density (n_e) in a low-pressure (40-100 mTorr) RF (13.56 MHz) SiH_4 plasma and the electron loss rate in the afterglow were measured with varying SiH_4 fractions in the SiH_4/Xe, /Ar, /He and /H_2 mixture gases. The behavior of electron temperature (T_e) was estimated from the relative variations of the excitation rate constants (K_<em>) for emissive rare-gas excited states, which were derived by combining the results of electron density measurements with optical emission measurements. The product k_<em>n_e generally increased with increasing dilution but the behaviors of the individual k_<em> and n_e differ considerably for different mixture gases. The results were discussed in terms of energy and particle balance consideration. It was found that the dominant electron loss process in the afterglow is attachment and that the major attaching species is not SiH_x (x=0-4) but some larger molecules produced in the plasma, even under the low-power (< about 5 W) conditions studied. The same attachment process was shown to have a significant role in determining T_e and n_e in the active plasma.
社団法人応用物理学会の論文
1996-06-15