Higher-Density Negative-Ion Production Using Magnetized SF$_{6 }$Plasma

Negative-ion plasmas have a big potential to improve production of high-quality LSIs in the high-tech industries by reducing notching effects during Si-etching. To realize the ultra-fine etching in LSI fabrications, a higher-density and stable negative-ion source is necessary. In a magnetized plasma column generated from an electronegative gas, it is known that negative ions are accumulated around the plasma column via radial diffusion [1]. In this study, DC discharge is applied in SF$_{6}$ gas to produce a plasma column with $B= $0.3 Tesla. The Langmuir probe method is applied for the diagnosis of the plasma produced in a metal chamber of 200 cm long and 21 cm diameter. Gas pressure and discharge current dependences of $n$(-) are observed. The radial density profiles are compared with those of CF$_{4}$. Negative-ion density is calculated using the modified Bohm criterion [1]. It is found that at $p= $0.13 Pa $n$ (-) in SF$_{6}$ plasma is $\sim $8x10$^{17}$ m$^{3}$, and in CF$_{4}$ plasma, $n$ (-) $\sim $3x10$^{17 }$m$^{3}$. This ion-ion plasma has $n$(-)/$n$(e) range from 100 to 900, and is attractive for applications. \\[4pt] [1] M. Abid Imtiaz, S. Tsuruta and T. Mieno: Plasma Sources Sci. Technol. \textbf{16} (2007) 324.