The plasma electron density in a symmetric confined capacitive-coupled plasma processing tool containing gas mixtures is studied as a function of two, combined radio frequency powers. For measuring we have used a floating hairpin resonance probe. The results show a linear increase in with power. Also the density is higher with an increase in power, in contrast with published particle-in-cell simulation results in argon where the plasma density decreased with increases in low frequency voltage, for fixed high frequency current [P. C. Boyle et al, J. Phys. D 37, 697 (2004)]. Analyzing the relative phase between radio frequency current and voltage, we observe slightly lower phase shifts at higher voltage, which is attributed to an increase in the real component of the current through the sheath. This is possible due to the increase in secondary electron emissions arising from ion bombardment, which is favored by an increase in voltage. We therefore conclude that the secondary electrons could play an important role in the discharge process.
Effect of radio-frequency power levels on electron density in a confined two-frequency capacitively-coupled plasma processing tool
S. K. Karkari, A. R. Ellingboe; Effect of radio-frequency power levels on electron density in a confined two-frequency capacitively-coupled plasma processing tool. Appl. Phys. Lett. 6 March 2006; 88 (10): 101501. https://doi.org/10.1063/1.2182073
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