A stable and high density F− negative-ion source by utilizing magnetized SF6 plasma

SF₆ magnetized plasma column, around which F^- ions are accumulated via radial diffusion, is generated by a dc discharge in a metal chamber. The Langmuir probe method is used to diagnose the plasma, and the density of the negative ions is evaluated utilizing the modified Bohm criterion. Parameter dependences of negative-ion densities across the applied magnetic field are investigated. Outside the electron-beam region (Φ = 20 mm) ion-ion plasma, where the ratio of negative-ion density to electron density ranges from 100 to 900, is produced. F^- ion density is found to be ≈ 8 × 10¹⁷ m^-3 at p = 0.13 Pa, B = 0.03 tesla. This ion-ion source is attractive for plasma etching.