Importance of repeller voltage on ion current generation in an arc ion source

Summary form only given. In an earlier study, we evaluated the importance of varying the magnetic field profile in the ELS source (Vandenberg et al., 1998). Here, we study the influence of the repeller voltage. A floating repeller will acquire a steady-state voltage close to the cathode voltage. A more careful investigation shows that the floating voltage depends on the magnetic field such that higher magnetic fields yield higher repeller voltages. Using a free boundary arc model (Keidar et al., 1998), we find that this can be explained by electron losses to the arc chamber. Thus, ion source operation at low magnetic fields, while being beneficial to source stability, results in less electron confinement. Biasing the repeller voltage positively and negatively with respect to the floating voltage affects arc current and the current extraction properties of the ion source. We find that a negative bias has little influence on the arc plasma properties, while a positive bias strongly modifies the mass spectral content of the ion source. As a consequence, a biased repeller source can have improved ion generation performance for semiconductor applications.