The energy distribution and flux of the fast neutrals and residual ions extracted from a neutral beam source were measured. Positive ions generated in an inductively coupled argon plasma were extracted through a metal grid with high aspect ratio holes. Ions suffered grazing angle collisions with the inside surface of the grid holes, turning into fast neutrals. The neutral energy distribution was always shifted to lower energies compared to the corresponding residual ion energy distribution. The neutralization efficiency increased with power, decreased with boundary voltage and. for thin neutralization grids, was almost independent of plasma gas pressure. The residual ion flux decreased with increasing hole diameter and hole aspect ratio. The fast neutral flux first increased and then dropped as the hole diameter was increased. Results were explained based on plasma molding inside the grid holes. (c) 2006 American Vacuum Society