Characterization of neutral beam source based on pulsed inductively coupled discharge: Time evolution of ion fluxes entering neutralizer

Low-energy neutral beam sources are very promising candidates for realization of next generation ultralarge-scale integrated devices. The use of pulsed inductively coupled plasma and surface (wall) neutralizer appears to be an efficient way of producing high-flux low-energy neutral beams. Measurement of the time evolution of ion fluxes entering the neutralizer plays an essential role in understanding and control of these neutral beam systems. Here the authors present a simple method for measuring the temporal dynamics of ion fluxes in neutral beam source described elsewhere [S. Samukawa et al., J. Vac. Sci. Technol. A 20, 1566 (2002)]. The method is based on the use of a low aspect ratio orifice in the center of neutralizer, magnetic filter, and Faraday cup. At some conditions, it allows (1) to measure the magnitudes of positive and negative wall ion fluxes in pulsed plasmas with an extremely high temporal resolution (better than 1 μs) and (2) to examine the difference in surface neutralization between positive and negative ions. The measurements show that neutralization of hyperthermal ions is mainly controlled by geometry of plasma sheath adjacent to the surface neutralizer; however, negative ions are neutralized more easily than positive ones. The experimental results for SF6 (ion-ion) and Ar plasmas in combination with dc/rf bias are reported