Role of reaction products in F- production in low-pressure, high-density CF4 plasmas

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 10(11)-10(13) 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.