Role of Reaction Products in F- Production in Low-Pressure, High-Density CF4 Plasmas

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Abstract
In this paper we report on the role of reaction products in F- production in low-pressure, high-density CF4 plasmas. The spatial distributions and temporal variations of F- density (n -), and plasma parameters in the discharge phase and afterglow of helicon-wave CF4 plasmas which had an electron density (n e) of 1011–1013 cm-3 were measured by the laser-photodetachment technique combined with a heated Langmuir probe. The relationship between the n -/n e ratio and the degree of ionization was investigated in the discharge phase. The n -/n e ratios in the plasma column of highly ionized plasmas were much higher than those expected from dissociative electron attachment to CF4, and n -/n e ratios were larger by several orders of magnitude in the outer region. The efficient increase in n - was observed in the afterglow and n -/n e was enhanced by increasing the discharge duration. It is concluded that the attachment to the reaction products contributes greatly to F- production in low-pressure, high-density plasmas.